The different names when it comes to Mac OS X are to differentiate actual OS version releases (Cheetah 10.0, Puma 10.1, ..... Snow Leopard 10.6, etc).. Each version release adds a wide variety of new features (Just like MS does with XP SP1, SP2, SP3). Don't forget, Microsoft uses 'code names' for all of it's OS releases such as Vista was codenamed Longhorn, XP was codenamed Whistler.
As a funny side note (to me at least) Windows Small Business Server 2003 was codenamed
Bobcat. Windows Small Business Server 'Longhorn' was codenamed
Cougar! Who say's Microsoft does not steal ideas from apple!
Actually there is a very interesting list of all the code names used on all Microsoft products over on
Wikipedia
Also keep in mind Mac's up until a few years ago used PowerPC (PPC) processors, so many of the apps that were written for 10.1, 10.2 may or may not work on newer Intel based Macs unless the software developers rewrote and recompiled the source code for Intel based Macs. This is something Windows users more or less never had to deal with (thankfully!) until i believe XP 64bit came out years ago for AMD's line of 64 bit processors as opposed to plain old Windows XP which was written for Intel 32 bit processors which dominated the market for so many years.
I use to work for Apple and got hooked on using Mac OS X.. After awhile XP started looking like a toy or fake OS to me (interface wise)
My experience with windows 7 has been great so far tho, so they must be doing something right over in Redmond
As far as calling Leopard 'an os that no one wanted'', I think is a bit out of line. Vista for SURE was the OS that no one wanted. It got so bad that people that were not tech savvy, but were in the market for a new laptop or desktop computer would second guess themselfs from all the bad hype surrounding Vistas poorly planned release.
And BTW, the Yes/No prompts in Vista and Windows 7 are a GUI-baed rip off of any Unix based OS such as Mac OS, Linux, etc. The idea of not making users by default administrators that can edit system critical files as they wish is a great one, but has been around for decades on any Unix based OS by only allowing root (or the superuser) change vital configuration files.