I don't know anything about software development but what would it cost to write the whole DDI to be both PC and Mac (and while your at it Linux!) compat? Too much, I guess, for the 10% or so to be a worthwhile market.
As for Gleemax, I have never had any problems on it (and I use IE, FF and Opera) so are all the Gleemax complaints from Mac/ Safari users? Just because I am nosey

Any issue with Safari is probably the same as you get some issues on other sites with FF, IE is the most 'slack' browser when it comes to reading your web page therefore will accept a lot more 'not wuite right' stuff. I would imagine Safari is quite strict. Who's fault is this? Well both Safari (because it is no use being too strict if it reduces your usefulness) and WotC (for not making Gleemax more compliant with web standards). Just IMO, and a guess from experience, rather than a fact from real knowledge about these things