Windows 9x (95, 98, and ME) were consumer operating systems. By consumer, I mean that they were built to be sold to the masses. They were not constructed with the same goals as a product such as Windows NT, and thus did not have true protected memory. If Microsoft had a superior product in hand (Windows NT 4.0 came out a few months after 95a did), why continue to build 9x OS's? There are several fairly rational reasons.

People compare Windows 98 to Linux all the time, and that is definitely an apples to gorillas comparison. No one compares Linux to Macintosh (as Linux would surely win). The real bout the UNIX crowd has is against NT. Windows 9x was built for speed, wide hardware acceptance, low requirements, and compatibility with a huge software base (as stated above). Protected memory (while obviously do-able), didn't fit in these requirements. So what if people have to reboot a few times, or a bad program would take down the computer. How different is that from DOS, or from Windows 3.1? Windows 9x was a transition series of OS improvements until we are at the bar we are today... protected memory, good networking, and server capabilities. The PC has come a long way.. let's keep the comparisons on an even plane.

*One noticable difference in compatibility was that undelete was expressly forbidden from running on Windows 9x.