There was a time when pagerank had just been invented and every other search engine OTHER than Google was still using the most relevant = most number of items on the page algorithm. Google was the clear leader then, nowadays it's less clear cut, but I always have and will use Google because their format works. It works, it works well, and apart from one or two probable tweaks to the algorithm it stays the same.
Compare this to msn search. Oh, sorry, it's just changed - windows live search. Oh sorry again, they're changing it so damn fast I'm struggling to keep up here, it's just live search now. Cool, so...
...sorry, news just in, they've changed it all around again and it's now called bing. Who did they pay to come up with that name anyway? I would've given them dingalong for free, and that sounds either just as bad or a bit better :-P
Thing is, Microsoft seem to be trying desperately to gain the tiniest footing in the search engine market by changing things around as much as possible. And now they seem to have fallen to the lowest of the low "we'll just copy Google's design and change a few bits" tactic. I'm not sure quite who they're hoping to win over by that, but the fact of the matter is Google is popular because it's good. And because it's been nigh on consistently good since they brought it out, people trust it, rely on it and they'll go back to it.
If Microsoft want to win over people to their searching, then they're going to have to pull something pretty revolutionary out of the hat - changing their design to look a bit more like Google every year and making a few changes to their algorithm to keep it a step BEHIND what Google are doing really aren't going to win many favours, and they need to realise that.
Thing is, if something revolutionary on the search front is coming, chances are it's coming from Google and Microsoft are just going to be spending years catching up again. This is the company that dismissed the internet as a fad before spending years and millions catching up with everything else, brought out aeroglass and claimed it was revolutionary but forgot what compiz / beryl had been doing for the past few years and worst of all - decided what everyone using office needed was, in fact, an animated paperclip.
Summary: Google FTW