Lots of people say they want to ditch cable TV for the Web, but can’t because they want to watch sports — specifically the stuff on ESPN, which has a hammerlock on much of the sports world.

Now they will finally get a chance: Dish’s new Web-TV service, which the company is formally announcing today, lets you stream ESPN, over the Web, for $20 a month.

Dish’s “Sling TV”* offering, which the company says will launch “soon,” also comes with 10 other non-ESPN channels, including the Food Network, CNN and the Travel Channel, and the ability to add more networks for additional fees.

But it’s very unlikely that you’re going to sign up for Sling TV because you want to stream Wolf Blitzer or “Chopped” to your iPad. If you get it, it’s because you want to see stuff like the College Football Championship, which is going to air next week exclusively on ESPN.

Put it another way: If ESPN wasn’t in this package, do you think Dish would be trying to sell it?

So to review: This is the year that you’ll be able to get HBO on the Web, without paying for any other cable channels, and ESPN on the Web, with just a handful of other channels. Throw in a Netflix subscription and you’re probably looking at a $50-a-month video package (you’ll still need to pay for broadband on top of that) that might please a lot of people — that is, people who want to watch cable-TV programming but don’t want to sign up for traditional cable-TV bundles.

That wasn’t supposed to happen for years, but here we are. It’s not the end of pay TV — the networks that are doing this believe they can sell this stuff on the Web without compromising their existing businesses — but it certainly could be the beginning of the end. At the very least, it’s going to be hard to roll this back.

Are there catches? Of course. And some of them we can see from the start:

Sling TV is a “personal subscription service,” which means you’ll only be able to watch it on a single device at a time — if you want to watch football and your roommates want to watch a “Law & Order” rerun, someone’s out of luck.

You can watch Sling TV on an actual TV, but it will require a bit of work. If you don’t want to watch the shows on your laptop or tablet, you’ll need a device that helps get Web TV to your flatscreen, like an Amazon Fire TV, a Roku box or an Xbox One; you’ll also be able to use a handful of Smart TVs that will support the service at launch.

One big omission from Sling TV’s launch list is Apple TV, which Dish says it would like to work with but can’t because of the rigid user interface rules Apple imposes on programming partners.** Apple TV users will be able to get Sling TV on their set top by using an iPhone or iPad and “mirroring” the stream to their sets, but Dish isn’t playing that up.

Sling TV also won’t do you any good if you want to watch your local broadcast stations or any of the broadcast networks. So no local news, no “Good Wife” and no Sunday NFL games, unless you’re going to buy an antenna. On the other hand, HD antennas are pretty affordable these days.

And there are also plenty of things we just don’t know about yet:

Will Dish really be able to consistently deliver high-quality streams of real-time programming? Streaming video works well a lot of the time, but we’ve seen plenty of high-profile Web TV events that have had problems in the last year. And even if Dish holds up on its end, there are lots of places for a stream to break down before it gets to your TV — your local broadband provider may have a hiccup, or you may have a crappy router, or you just might be confused about how to use your Google Nexus player. But if you want to watch Oregon-Ohio State and you can’t, you won’t care why — you’ll just blame Dish.

Is Dish committed to keeping this at $20 a month? It’s hard to see how Dish can make a profit at that price, since ESPN on its own usually costs pay-TV companies $6 a month. Dish says it’s committed to keeping its pricing intact — but if you’re suspicious of the promises a pay-TV company makes I can’t blame you.

What happens if people really sign up for this in big numbers? After all, the four programmers Dish has signed on for this package — Disney, Turner, Scripps and A&E — are all full-fledged members of the TV Industrial Complex and have made a very good living in the old paradigm, where people pay a bunch of money for a bunch of networks, whether or not they watch them. Wouldn’t the success of Sling TV threaten their existing business? Dish, for its part, insists that it plans to sign up “millions” of people for the new service. But sources say ESPN has a clause that gives it the ability to get out of Sling TV if the service signs up a certain number of subscribers, precisely for that reason; I’m assuming the other programmers have one as well.

It’s also possible that Sling TV simply won’t get that much pickup. After all, there are lots of ways to get relatively cheap packages of cable TV, and most of them don’t seem to be very popular. Maybe the people who say they don’t way to pay for pay TV really don’t want to pay for pay TV, no matter how it’s priced.

But my hunch is that HBO and ESPN are going to find lots of interest in what they’re selling this year. And that when they do, they’re going to find lots of other networks that are happy to join them. This could be a very big deal.

* Dish wants you to know that Sling TV has nothing to do with its Sling Media and Slingbox products, but doesn’t explain why it used the same brand.

** I’ve heard other Apple TV partners gripe about Apple’s design edicts as well. On the other hand, plenty of Apple TV partners, from ESPN to HBO to CBS, seem to be able to deal with them.