Hotmail/gmail stripping css?

[r988]

I find that html emails sent to hotmail and gmail addressses tend to strip off the css text formatting, any one know why this is? It has been suggested to me that their own css formatting is interfering with that in the email. Simpler webbased mail sites and outlook display fine. I have tried both externally linked css and embedded but it makes no difference. It's not a huge problem, just mildly annoying and something that I was curious if anyone knew the answer to.