fz20 ain't as heavy as you think... it is only about double the weight of tz1.
and what do the lens design/focus and zoom wheels have to do with the shutter/aperture dial of 350D? :dunno:
If you are talking about the lacking of aperture/shutter mode, I think that is becos tz1 is design for a casual/snapshot shooter thus the missing of those "manual" mode.
and btw, i don think even if they place a hotshoe mount on tz1 current design, no one will want to mount a flash that is heavier and bigger than the camera itself.