Why can't download and seeding threads sync automatically?

[smw]

Whenever someone asks if there is a way to avoid "checking", the answer is inevitably to "shut down gracefully". But this isn't always possible; Windows crashes, hardware crashes, power failures happen, uTorrent crashes or sometimes hangs, or we just forget. If I do a graceful exit, uTorrent syncs all threads before shutting down, and this happens very quickly. Why can't uTorrent simply run the sync process against every incomplete or just completed thread every couple of minutes, and on restart, just ignore all incomplete blocks that have been uploaded since then? You have a process to keep track of which blocks have been written, but obviously it's imperfect, since a thread that's been seeding for several hours can still get checked after a crash and restart, unless you shutdown and then restart the uTorrent process.