Just in theory when updating several apps from the Market (or other activities requiring use of /cache partition) it is possible that the /cache is filled with data and the device stucks at a point when it has no more space available to write. Rebooting to recovery and wiping /cache solves the problem. But if in that moment, when the app is downloading to /cache and another app is written from /cache to the /data partition at the same time, disconnecting the power source (battery pull) can interrupt the process making this partition unavailable (example: if you take out your USB flash drive from the PC while writing data on it there is a great chance to destroy it - tested myself ) The ext4 file system provides a protection for such cases by the way it is managing the writing process - reference here.
What i don't understand is this - when downloading multiple apps from market (i had 2 - Angry birds, ES file explorer), the phone goes to sleep mode, and NEVER wakes up. No ADB, no 3 key combo, NOTHING. This leads to an unavoidable battery pull, which results in corruption like you said above. Why does the phone enter this "Sleep of Death" if you may call it? What the hell is the problem? Also, why not other HTC devices? (for that, i guess the answer is the unique slide out battery, only in 2 other devices - Bliss and Radar, whose battery can't be removed). If we can solve the "Sleep of Death" mystery, we'll get this issue out.
(More info - http://bit.ly/rXhDRR and http://bit.ly/v3lsS6 )
Also, DS (and all new HTC devices) are EXT4 by default. Flashing (not s-off'ing, but flashing a ROM after that) changes back to EXT3. That is probably why my phone survived the battery pull i did as said above. (It was freshly s-offed by XTC Clip, stock ROM).
Finally, i think this only happens to devices with already screwed eMMCs. Mine survived many battery pulls after the first one. The screwy ones are region specific. I never read anyone from India had the issue.