Ever since the introduction of Microsoft Office 2003 it has been possible to distribute documents that can only be used in the way that you want them to be used — such as limiting who can copy, print or forward the information. This type of control, however has been easy enough to defeat with a third party reader that ignores the "Information Rights Management," which is really just a bunch of plain text XML, as Cory Doctorow explains at Information Week. So IRM is really not about security in the first place.
"The current version of remote attestation facilitates the enforcement of policies against the wishes of computer owners. If the software you use is written with that goal in mind, the trusted computing architecture will not only protect data against intruders and viruses, but also against you. In effect, you, the computer owner, are treated as an adversary." -The E.F.F.'s analysis on the new techniques
Microsoft, naturally, would like to end the ability to use third-party readers like OpenOffice all together, and is working to develop an industry standard that will allow your motherboard to take digital signatures in order to prove that your software is not tampered with. Security is touted as being the reason for all the work, but it seems clear enough that a uber-vendor-lock-in is attractive to the Men of Microsoft.
The Electronic Freedom Foundation has a typically well-researched document on the background of the situation, with some proposals for mitigating the vendor lock in issue.