First lets define Android fragmentaionn. In the tech world it applies to the 6 different versions that exist in the Android ecosystem.
Donut, Eclair, Froyo, Gingerbread, Honeycomb (tablets only), and Ice Cream Sandwich. It also refers in part to the many different devices that are available with different specs (CPU, screen size/density, available memory).
If you own any Android then you've had one of these versions. You may have had more than one actually, especially if you have rooted or own a Nexus branded device.
One of the cons to fragmentation is that developers have to take into account the varying specs that each device may have when creating their application. Not only would concern about a device being able to run the app, nut will it be full screen, how much internel memory will it take up, and many other variables. This sometimes means that a developer will either end up neglecting a portion of android owners, or have to create several versions of an app.
See this article: http://mashable.com/2012/01/03/android-fragmentation/
Keep in mind that usually when you hear something negative in regards to fragmenting it is related to updates to whatever version is out at the time. Fragmentation was big when Gingerbread rolled out, as it was bandied about more and more as ICS came to be. I can promise we will still be discussing it next year as Jelly Bean beats release.
First up are those with older tech that are upset that the newest os won't run on their device (Galaxy S owners anyone?). In my opinion one has to understand that as new features are added (that may not have been considered two years ago) it has to be accepted that said features may need more memory/horsepower than your device can muster. Like it or not this IS how the tech world works.
The other side to that argument lies with device manufacturers who take the current os and apply their branding to it. If you own an HTC then you have Sense. If you own Motorola then you have Motoblur. Samsung, Touchwiz.
Love them or hate them, these additional overlays delay updates because they have to be tested, and in some cases can't be squeezed into some devices. They add graphical and functional additions that can raise the footprint in internal memory quite a bit over stock. For example, a stock ROM on the EVO 3D is well over 400mb, and a pure Gingerbread can be as low as 150. (Numbers from memory, however I believe difference holds).
So as an android owner, what do you do about it? In a nutshell, don't sweat it. If you are a casual user you honestly probably just found out about it during this read and will never have any issue. There will almost always be an apparently that does what you need and your device will usually fit your needs. If you are a power user and geek, just root. Galaxy S owners were told they wouldn't get ICS, but itss available to install by flashing.
If you have any comments/refutes, well thatss what this forum is here for.
I blame the manufacturers. Their need to differentiate themselves from the rest of the pack has hurt Android in some ways but improved consumer appeal. When I first got my Nexus1 I showed it off to everyone I knew. The reactions were a mixed bag; some liked it but others didn't. After a few months of running it stock Froyo I began my journey into the world of root, Roms, and cyanogen. Once I loaded an HTC Sense Rom reactions toward my phone changed, everyone loved that big clock and the rain drops forming on the screen to be followed up by a windshield wiper. "did you get a new phone"? No. I installed a rom. "a what"? Go play with your razor, dude.
I guess the point I'm getting at is that vanilla Android is for the small crazy few of us that make up a tiny percentile of the market while those other citizens need more eye candy, should I say; an instant layer of gratification. The manufacturers ruined Android for me. Until they release Nexus phones on all carriers at the same time I don't see myself going back to Android. I want OS updates the day of their release, I want all apps to work, I don't want my phone to feel aged in 3 months, I want support from a brick and mortar store so when I have issues I can swap my phone for a new one that day(off topic but as long as I'm rambling...) and I want my phone to at least last 2 major OS updates!
Android in itself is a different beast compared to the iPhone. It Relies on specs, different models, prices, form factors but do we need to sacrifice longevity for choice?