Josh Miller/CNET

Say it ain't so, Samsung.

When the Galaxy S5 came out last year, I wrote about how I was thankful that Samsung hadn't dramatically changed the design of its flagship smartphone, keeping its replaceable battery and storage expansion slot, both of which could be found underneath its removable plastic back.

Yes, Samsung took a lot of heat in some quarters for making a flagship phone that didn't seem to match the premium look and feel of the iPhone line. But Samsung didn't sacrifice functionality and flexibility for swankier looks. That flexibility -- the removable battery and expandable storage in particular -- is ultimately what differentiates Samsung's Android phones from Apple's iPhones. And I said that's why I'd never buy an Android phone that didn't offer those features.

Well, say goodbye to that differentiating factor. Samsung's new Galaxy S6 and Galaxy S6 Edge , both announced earlier today at the Mobile World Congress show in Barcelona, have have sleek "unibody" designs expected of today's flagship smartphones. And while the entry-level models will come with 32GB of internal storage (rather than 16GB, as on the iPhone), there's no expansion slot for additional storage and the battery isn't user-replaceable. That also means you can't carry around an extra battery to swap in case you run out of juice.

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Battery blues

Clearly, Samsung is girding itself for these criticisms. When challenged by my colleague Jessica Dolcourt, Samsung reps noted that the battery "hard resets" by pressing and holding down the power button. And the fact that the S6 models offer both super fast charging and built-in wireless charging are meant to ameliorate the battery issue.

True, an embedded battery does have its benefits. It allows designers to slim devices down those extra few millimeters (see Jessica Dolcourt's " It's time to kiss the removable smartphone battery goodbye") and embedded batteries typically offer longer "useful life" over time.

For instance, according to the folks at batteriesinaflash.com, "Apple estimates that its sealed battery laptops only lose about 20 percent of their ability to hold a charge after 1,000 discharges of the battery." The same site says that many laptops see a large dip in battery life after less than two years of use. The same holds true for smartphones with removable batteries.

But if anything goes wrong with your iPhone's battery, you're supposed to take it into an Apple Store or an Apple-authorized repair shop to get it replaced (Apple charges $79 for iPhone battery replacement and $100 for an iPad battery replacement) Meanwhile, I can pick up a new or spare Samsung-made S5 battery for around $25 and an OEM version for around $11. Not bad.

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More GBs, please

The other plus to the S5's removable back is the ability to access the storage expansion slot and add storage. As people use their phones to shoot more video -- and watch more of it -- your storage can dry up pretty quickly, especially if you have a bunch of games and photos on your device.

Again, Samsung reps were quick to point out that the capacious storage options on the S6 line -- 32GB, 64GB and 128GB -- should nip that problem in the bud. But I'm sure, just like Apple does (much to our continued chagrin), Samsung will charge something like a $100 premium for each storage step-up. That's considerably more than Samsung's 64GB PRO Class 10 Micro SDXC card, which costs about $50. Step-down versions of the memory cards are available for even less, and these cards are getting cheaper every month.

What about the cloud? Yes, the Galaxy S6 models include two free years of 115GB Microsoft OneDrive storage, which is one of many cloud archiving options available. But I know plenty of frequent travelers who store dozens of movies on their phone's memory card (don't ask me where they get those movies) for enjoying in those connectivity-free zones like flights or cruises. Or even just hotels with crappy Wi-Fi.

End of an era?

With previous Galaxy phones, the removable back also tied into other accessories. You could swap in backs with integrated front covers, backs that left room for extended batteries, and a back that allowed for wireless Qi charging -- to name a few. Wireless charging is now built into the S6, which is nice, but it's a small consolation prize. And weirdly, these new models, despite being "sealed," aren't waterproof like the standard S5 is. (That said, I expect a "rugged" waterproof S6 model later this year.)

Consider too that Samsung made removable batteries a cornerstone of its anti-iPhone "wallhugger" ad campaign, even going so far as to show a real-time battery swap in one of the TV ads (embedded above). Up to now, it was a feature endemic to the Galaxy brand. Oh well.

In the end, as slick as the S6 might look, it marks a victory of form over functionality and flexibility. That flexibility is what differentiated Samsung's Android phones from Apple's iPhones. Now it just comes down to an operating system, and I'm not sure that's a battle Samsung's going to win.