Apple are the latest participant in a very limiting trend that I've seen on the Internet and that's developers making the choice to simply not support Internet Explorer for some functionality. I pick Apple because of it's high profile warning when you access MobileMe using Microsoft's browser. Instead of taking the time necessary to code for the most popular browser in the world they just stick up this warning and think that that is the way web development works. Well I'm afraid it isn't. In the end it would be much easier to be able throw up a message stating that the service doesn't work with Safari, an unsafe and unstable browser with a tiny share of the browser market, or Firefox, competent but again a browser without a majority share. I'm fed up with seeing web pages telling me that the developers couldn't be bothered programming for the majority of their viewers and if they don't care about providing me with a fully working service then why should I bother using it at all. If they can't develop for Internet Explorer then say so but don't blame it on the browser.
And for all the fan-bois out there who think that this is the behaviour that will bring down the Redmond Giant and is being done to make some sort of stand then just bare in mind that the iPhone and all iPods are fully compatible with Windows with no difference in functionality between Mac and PC. The major products are compatible because they won't sell if they aren't and profits are what matters most, bottom line. Minor services don't matter as much and obviously get less attention so ask yourself is your service minor and insignificant or will it be the next big thing? If the answer is the latter then sit down at you development environment, remove the warning message and get to work.