Not really: I looked at the cron source when the 770 was released and it quite properly sleeps until the next alarm - so shouldn't be too much of a battery hog. Although it wouldn't provide a mechanism for waking up the device from power-off, like alarmd without some of the code in alarmd.

alarmd is the right way, as you say, but it's just Nokia's NIH syndrome rather than any technical reason (a DBUS API to cron would be achievable, but harder work without an XML backend).

Similarly, a crontab interface to alarmd would also be achievable (but for very little benefit).