There are many factors to consider here:
1) When XP was released, the Internet was not as accessible. Therefore, (mis)information didn't spread as fast.
2) No matter how votes sway, complaints are always louder than compliments. The Internet is far more widespread, so negativity becomes even louder.
3) People complained about XP upon its release. See point #1 for why it didn't seem as rampant as that of Vista and, to a lesser extent, Win7. For all we know, the complaining could have been as loud. It's just that there weren't enough ears for all of it back then...
4) XP replaced a negatively-received Windows Me, a hit-and-miss Windows 98 (mainly because this was the only fall-back for consumers that didn't want Me), and a positively-received Windows 2000. XP fit the bill quite well for the two 9x kernel OSes, effectively sending 9x to its grave. 2000 was more hit-and-miss: it didn't really offer much else in comparison to 2000 back then (Remote Desktop was nice, though).
5) Vista was replacing a positively received XP only (which people were complacent with, as it had no replacement for six years of it run!). It had some big shoes to fill and, for the most part, failed to deliver on that.
Its only real contributions were a better security model (even with UAC's annoyances, it's nice to be able to actually run programs as a standard user...just type in an admin password!), a push toward mainstream 64-bit support (XP 64-bit, aka. stripped down Server 2003 with 64-bit code, didn't have much consumer hardware support), and better Windows Media Center/Tablet PC support (want 64-bit Media Center/Tablet PC? Vista was your only option).
6) Windows 7 is replacing a negatively-received Vista and a positively-received XP. It is also the first Windows OS to actually run leaner than its predecessor. It's also benefiting from all of the fixes that were made to make up for Vista's shortcomings (file copy speed fixes, delayed Superfetching on startup) and has the added benefit of being able to use XP Mode to get around compatibility problems (I'm sure they could have backported this to Vista if they wanted to...)
7) The biggest complainers against XP were those that used Windows 2000, Macs, and Linux distros. The latter two are going to complain no matter what simply because they're already decided that they don't like Windows. The Windows 2000 complainers complained about the very thing that people in this forum are complaining about Vista and 7: bloat! 2000's minimum CPU speed requirement was 133 MHz while XP's was 233 MHz. This was back in 2001 in which a 100 MHz difference was XBOX HUGE! Now that the hardware has far surpassed the point where 100 MHz makes that significant of a difference, we don't hear as many complaints about XP bloat...
8) Finally, "software bloat" is in the eye of the beholder. Some people want Windows Media Center for their HTPCs. Others see it as a waste of resources. Some people like Aero. Others see it as a waste of resources. Some people like Windows Mail (which is not included in Windows 7). Others prefer to use web mail, Outlook, Thunderbird, etc. "Software bloat" is nothing more than developers trying to please everyone and, in the end, pleasing no one. Some people like indexing to find their TBs of files. Others see it as a waste of resources. Some people like Superfetch to use their unused RAM to retrieve their most frequently used programs faster. Others see it as "OMG, VISTA/7 IS USING A MACKTRUCK OF MAH RAMMERZ! XP IS BETTER!"
...then again, Superfetch is probably one of the most misunderstood (and polarizing) aspect of the Windows NT 6.x operating systems...
Of course "code bloat" is a different story altogether (which I think Vista had a lot of and Windows 7 fixed).