If you're an uber-geek and know what you're doing, then you should use geeky, dangerous tools like PyWallet to do what you want to do.
Agreed, except those doing web services that might depend on this feature are left with either non-official clients or patching the official ones, which gets complicated to maintain in a stable, well tested way.
The current import patch needs work to be of practical use to web services-- it does a scan of the entire blockchain to find transactions to the newly imported key (and keeps the wallet locked that entire time). For any sweep/import solution to be useful for more than once-in-a-blue-moon use, an index of pubkeys to transactions involving those keys should be kept.
It seems to me the "sweep now, and re-sweep every once-in-a-while" functionality would work nicely for web services. Can you describe a use case that wouldn't work?