That would be my guess as well -- but one client who came to us had success with this very naive approach about a year ago, back at the very beginning of Google's "aging algorithm". Because it worked for them (moving to a brand ne domain name) I wasn't going to mess with their success.
I'm thinking that part of the 301 problem comes from Google working against manipulation attempts, and not just looking for "aged" domains. Google's handlinh of 301s is certainly a complexity, rather than a simplicity like Yahoo's relatively straightforward approach.
Because I did see one successful use of a non-301 approach using a simple link and 404 pages last year (the old domain went completely offline within 2 months), it does make me wonder. Maybe the more technical we get, the more we look like we're attempting "search engine persuasion."