IE only had a horrendously slow development cycle with minimal resources committed after it became a monopoly. Up until that point it was regularly updated with features and bug fixes.
I doubt that Chrome/WebKit will stagnate if it becomes the de facto standard but I'd rather it didn't have the chance and I'm constantly amazed that so many comments on HN seem desperate for one browser to rule them all.
IE was always that way, actually. Please check their release dates. They were very slow by standards we expect today. After 6, they did suddenly disappear for years, but again, this is a Microsoft problem.
It was also closed source, so nobody who found a bug could just go fix it. You had to ask Microsoft, nay beg Microsoft, to fix it for you. And they didn't.
These effects compound one another. The result is that MAJOR bugs become features.
You're wrong, but I guess you're too young to remember and can't be bothered to learn anything.
The IE team produced 7 versions in six years and there were some very substantial advances, including a new layout engine (Trident). They also did Mac and Unix versions, a mobile version, and a tabbed version for MSN (before iE had tabs).
IE certainly developed a lot faster than anything else on the market in the 1990s, bearing in mind that Netscape took three years to get from 4.7 to 4.8.
Safari entered the market late (2003) and still took the best part of seven years to make it to version 4.