It's a standard, industry accepted service which Nokia refuse to support. Many N900 owners have it high on their wish list because they already have accounts on corporate servers that they want to access (little point carrying around an "all in your pocket" mobile computer if it can't access your work email or calendar). Even if you don't have (or want) access to a corporate server, there are plenty of suppliers offering MSE services (including Nuevasync which the OP was using) which give similar protection and peace of mind (and push email - seeing as the N900's IMAP implementation is also half-baked).

Point is, if you advertise something as MS Exchange 2003/2007 compatible, then you shouldn't be surprised when customers see that to be a nod towards corporate use, and therefore expect it to work with commonly implemented policies which no security concious enterprise would be without.

And seeing as those services are widely available and adopted (and even supported by Nokia themselves in other versions of MfE), to me it seems ludicrous to expect users to invent something else from scratch when there would be no need if Nokia had done their job properly in the first place.