Not true. I made an argument with Microsoft that they are obligated to fix bugs in their software, free of charge, and they appear to agree. Hense why you can call PSS and request to get the latest Hotfix or SP and not be billed for it.
Upgrades to new versions and other "enhancements" to the software (which we havn't seen, because they're all put in to hotfixes along side the bug fixes) is what the maintenance contract gives you. You also get newsgroup-based tech support in the private newsgroups, access to CustomerSource for customized receipts, reports and the knowledge base, and discounts on telephone tech support.
I do believe everyone should get the maintenace contract, but a lot of my customers have a hard time justifying the price when there hasn't been a new version released in over 2 years. Unless the customer has someone working for them who is computer-literate, they will never use the resources that the maintenance contract offers them because they just call me when there is a problem (which isn't all too often).