Windows games have to run on thousands of different configurations with very few problems, så it's probably not a big deal.
Not the same at all. Windows game programers know that their user has a mouse, a keyboard, and a monitor that is probably more than 1000 pixels wide. These are all assumed to be true for any Windows game you may write.
Cell phones are DRASTICALLY different from one another. Some feature a pointer controlled by a button or knob. Some feature touch screens that may or may not allow multiple touch points. Some have keyboard and buttons. Others barely have any. Some have EDGE connections only. Others have wi-fi.
Screen size is also a problem. With Windows, the screen may be bigger or smaller, but you can count on a minimum size. Anything larger than that, you just spread stuff out. With a small screen, every little pixel counts when it comes to good design. With so many choices, they'll have to optimize for one size, and wish good luck to people running different sized screens.
The point is not that these programs will run poorly on other phones. The point is that you'll start to see Android apps that only support CERTAIN phones.
And that's where the true mess will arrise. With the Apple App Store, you can buy anything for the iPhone. With Android you'll be sifting through thousands of apps, of which probably 50% work on your phone, and 50% don't.
Now, this is Google, so hopefully they'll feature really nice ways to browse and sort the store items. Maybe filter it down to just your phone model. I do think it will work well for the user. Google is good at that.
But that's the user. It does not sound easy for the developers, so it may take some time for them to build up a good store since it's going to be challenging for anyone trying to build Android apps.