Well, you can get some interesting data over at shadowserver.org -- from their Viruses page:
"It is difficult to not compare one vendor to the next due to how we have the data structured on the pages. It would be impossible not to try and derive conclusions from those results. While that is the case, our goal is not to create a real comparison site for everyone to try and compete to see which AV vendor is better than the next. There are a multitude of those already, each of which have their own sets of malware to test and rules that they follow for complete their testing. That is not our purpose. We do not have a specific set of malware to test. We instead gather in new malware daily and test it against the different vendors.
The versions of AV engines that we have are as new as the vendor can provide us and updated at least hourly if not more frequently. But they are gateway or fileserver products for the most part. We do have plans for using full consumer AV applications as well, but that will take time and much more in donations to allow us to build the back end for that. We will get to it, just not today. "
At the moment Microsoft's yearly stats are at 65.8619 %, their 180 day stats are 70.2719 %, their 90 day stats are 79.0509 %, 60 DAY 83.0405 %, Monthly 81.2884 %, Weekly 70.7138 %, & Daily 81.9642 %. While I was looking through their data the last few minutes it updated, & figures changed, so this really seems a dynamic, very real world view. For reference the winner [if you can call it that] had a 90+ % detection rate in the 90 day & shorter periods.
Check it out yourself & you'll see Microsoft is neither near 1st nor last place, so while they have a right to complain, perhaps they're blowing their own horn a bit too loudly. :)