Isn't. Vista just a prettier version of ms xp?
No. Vista has a completely reworked kernel architecture with improvements pretty much at every level. XP was more or less a prettified version of 2000 (which isn't to say they <didn't> make improvements, but nothing nearly as colossal as Vista did.
Why is it a mistake?
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The failure was more marketing than technical. Also, a lot of the changes that improved the OS also meant that low level internals worked differently. Turns out, however, that a lot of big name companies decide to use the undocumented internals and rely on a specific memory arrangement, so those programs break. The same thing happened with the switch to 9x->XP, since a lot of 9x APIs didn't have strong parameter checks. The preconditions were listed, but due to performance considerations they were assumed, which meant that in a lot of cases invalid arguments seemed to work fine. NT isn't as lax and would actually return an error and set the last error to something like ERROR_INVALID_PARAMETER if, in fact, you try to pass an invalid parameter. This was actually a common thing for applications but was mostly mitigated with appcompat shims. I imagine that a good portion of the larger size of the install that people like to poke at for Vista could very well be attributed to appcompat shims for developers who assume that if it works on one version, it will work on all later versions. This is mostly true, but only if you follow the documented APIs. Once you start screwing around in the low level details (to the point of actually manipulating the undocumented Window structures used by the window manager, making assumptions about how memory is laid out, and so forth, all bets are off.
If you ask me, given the number of changes to the OS, I'm surprised there were as few problems as their were. the appcompat teams did pretty well to shim the more popular applications. It's a bit sad that MS has to do this patching, since it was the devs of the game or program that screwed up; but at that point, they already have their customers money so they don't care. But, if MS doesn't do that, people will upgrade, find their dinosaur shooter game no longer works, and blame the update, since it worked before.
I didn't see Vista's reception as being any worse (or better) than XPs. The cries of "I'll stick with XP forever" ring hollow when those same people were animate that they would use 98SE forever when XP was released. (or even back to saying the same thing about DOS 6.22 and Windows 3.1 on the release of Win95) The tech industry by and large sometimes appears to have the memory of a goldfish.
Even now I'm surprised how many programs work properly on Windows 7 x64 that are from the mid-late 1990's. Of course DOS or 16-bit programs don't work, but I've had a lot of success with other games. (especially after unregistering gameux.dll, which apparently stops games from loading when the machine has no net connection...). I don't recall any specific problems I personally had with Vista that were fixed with Windows 7. It has a lot of visual improvements and UI tweaks, but by and large it's a Vista relaunch, which let's people like Windows 7 and also hate Windows Vista without thinking too much about the hypocrisy of doing so.
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