The main reason is to add PSN+ support to the systems. The PS3 also has updates to the photo browser adding uploading and downloading of Picasa and Facebook galleries, and theres now a video editor allowing for upload to Facebook and Youtube and such. Because I know you were all clamoring for video editing on your PS3.
The PSP update might be a little more interesting. It doesn't seem to add anything in particular, but it now has the ability to sort installed games by type. The interesting part are the options: PSP, Minis, Playstation (PSOne), PC Engine, and NEOGEO. Looks like we've got some new emulation options on the PSP coming soon.