I have been experimenting with the python command-line utilities by running
git clone https://github.com/ethereum/pyethsaletool
This consistentlyproduces 129-character encseed values.
I also tried downloading a wallet by clicking "buy ether" on ethereum.org and got a wallet with a 1249-byte encseed.
Why the huge difference? I am now suspicious of the command-line tools!
(Incidentally, shouldn't they also be using something like Crypto.Random rather than os.urandom?)