That list doesn't reflect the reality, which is: 1 - The need for service packs depends partly on how half baked the RTM was. Seriously, how many of those versions were usable and stable from day one? W7 was far better out of the box than Vista, XP or 2000 was. Dunno about NT 4.0 or NT 5.2 since I never used the RTM versions of them. 2 - How much better did W7 actually get with SP1? Sure, you didn't have to install loads of updates, but the overall impression was the same as with RTM. W7 RTM was stable. 3 - The reason why XP SP3 exists, why Vista was delayed, and why Vista RTM sucked was all because MS dropped the ball back then, simply put. 4 - The reason for why there are six service packs for NT 4.0 is partly because back then you didn't update the OS over internet the way we do it today. You used floppies or a CD with the service pack to update, the service packs were much smaller and came more often. SP1 was 1.4 MB large and came SEVEN WEEKS after the launch of NT 4.0.. As a contrast, W8 got a 170 MB large cumulative update this week from WU, before launch. That update alone is larger than all the service packs for NT 4.0 combined! I expect one more SP for W7, at most.