Here are some stats of browser/OS activity on APUG. I wouldn't say Macs are at 90%. Maybe he means digital photographers? seems like they would use macs more.

Top 15 of 1545 Total User Agents

# Hits User Agent

1 221813 14.60% Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)
2 198216 13.04% Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; .NET CLR 1
3 93730 6.17% Mozilla/4.0 (compatible; MSIE 6.0; Windows 98; AtHome0107)
4 75788 4.99% Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0)
5 75073 4.94% Mozilla/4.0 (compatible; MSIE 6.0; Windows 98
6 40759 2.68% Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; .NET CLR 1
7 38078 2.51% Mozilla/4.0 (compatible; MSIE 5.5; Windows NT 5.0; H010818; .
8 33985 2.24% Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; Charter B1
9 32535 2.14% Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en-us) AppleWebKit/8
10 28974 1.91% Mozilla/4.0 (compatible; MSIE 6.0; Windows 98 Win 9x 4.90)
11 27112 1.78% Mozilla/4.0 (compatible; AvantGo 5.2; FreeBSD)
12 26773 1.76% Mozilla/4.0 (compatible; MSIE 5.5; Windows NT 5.0)
13 24816 1.63% Mozilla/4.0 (compatible; MSIE 5.5; Windows 98 Win 9x 4.90)
14 22216 1.46% Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)
15 20255 1.33% Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; Q312461; Y