Microsoft needs to look beyond the PC and deliver IE9 to every tablet on the planet.

Microsoft has successfully delivered its best Internet Explorer ever, IE9, but I have this nagging feeling that it may be too late.

Let me put it another way. Imagine you're having a delicious piece of apple pie and you realize that the only thing that would make it better is an ice-cold glass of milk. Someone goes out for milk, but by the time it arrives, you've already finished your pie, cleaned the plates and left the room. Today, I'm wondering if is that cold glass of milk.

With 40 million downloads on the beta and release code and , Internet Explorer 9 is shaping up to be a success. There are hundreds of millions of Windows users in the world, and I bet many will want to download IE 9 (Windows XP users can't run IE 9. There must be a lot of frustrated netbook owners out there today.) With all those potential customers, why am I worried? Heck, why should Microsoft be worried?

Blame the iPad

We're entering a "post-PC era," Apple CEO Steve Jobs told a packed auditorium as he unveiled the iPad 2 last month. I was in that audience and thought it a bold statement. Jobs is, however, at least partially correct. Things are changing fast in the PC space. There are still millions of PC users out there, but the activity, excitement, innovation and interest is on mobile devicesdevices that don't require a mouse and keyboard. On the other hand, "PC" equals "Personal Computer," and the iPad is clearly a computer and also very personal.

I suspect, though, that Mr. Jobs was really trying to use "PC" as a synonym for Windows computers. In that case, this all gets more interesting and brings me back to my concern about Internet Explorer. You see, Jobs is right: Windows and the software that runs on it, including Internet Explorer, is becoming less interesting by the minute. First of all, all the latest browsers now look and work the same (I challenge you to, at a glance, tell the difference between IE 9 and ). Secondly, they're largely irrelevant for the hottest gadget space: Tablets. Let's look at some of the top products:

The iPad 2: It runs Apple's iOS, Safari, and virtually no Microsoft client-based software.

The Motorola Xoom: This Android 3.0-based device has a Linux core and its own browser client.

The RIM Playbook: It's also running a new mobile OS, QNX, and also has its own home-grown browser software.

The HP TouchPad: The first and possibly most important Web OS device is not running Windows and will have another unique browser.

Just look at the list. No support or interest in Internet Explorer. Obviously there are a few Windows tablets on the market, but consumers aren't buying them.

Perhaps I'm overstating the case. Compared to the desktop and laptop market (even compared to the handset market) tablets are tiny. It won't remain that way for long, though. "Which tablet should I buy?" is rapidly replacing "Which computer should I buy?" This doesn't mean people aren't buying desktops and laptops, but the commoditization (the move toward roughly equal components with fewer and fewer differentiating features) of those two categories means many people can buy almost any computer without worrying if it will satisfy their computing needs. People no longer want PCs, they often have to have them to get things done. They want tablets. They see them as cool, sexy, fun. On tablets they can buy apps like popcorn: popping one after another into their tablet's mouth while only paying 99 cents or less for most of them. Desktop and laptop software is still, usually, more expensive and it's poorly categorized on the Web and on brick and mortar store shelves.

Microsoft isn't unaware of the changing world. They have a mobile play: Windows Phones. Plus they're preparing to cross the platform Maginot Line and march into ARM- based processor support just so Windows 8 can run on future tablets. In theory, that would put IE 9 or some form of it on ARM-based tablets (maybe someone will jailbreak an iPad 2). Unfortunately, that operation is a year or more away. In the meantime, what is Microsoft doing to get Internet Explorer 9 on mobile devices, aside from what you'll find on Windows phone? Nothing.

Sometimes I wonder if Microsoft has forgotten that it's a software company. They should want Internet Explorer to run on every platform.

When I asked Microsoft's corporate vice president of Internet Explorer, Dean Hachamovitch, about whether or not Microsoft was working on a version of Internet Explorer 9 for the iPad, he smiled and answered slyly, "The browser is only as good as the OS it runs on. We build Internet Explorer for Windows Class OS." He then paused, smiled at me again and added a more succinct answer, "No".

It's a clever response from Mr. Hachamovitch, but, in my opinion, the wrong one. For now, the iPad only has Webkit wrapper-based Safari "alternatives" like LastPass and SkyFire. But that doesn't mean it can't run alternatives. If Internet Explorer is to remain relevant, it has to be on the iPad 2 (if Apple would allow it) or some other tabletyes, "IE the App". I urge Microsoft to reconsider, or IE 9 will be the delicious glass of cold milk, left alone in an empty room.