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.
Nobody shipped major versions "yearly".