prosumer has M functions, that's y it is called prosumer,
user can manually set the ISO, Shutter Speed, Aperture values..
I used to have canon s3is, feature wise, s3is still beats my d40,
it has exposure bracket, focus bracket, interval timer..
i change to dslr becoz i wan better noise control, wanna try different lenses.
and for most prosumer, u dun need to change the lens, the lens is built for all-purpose, from macro to tele zoom, 12x zoom is sufficient for most of the time..
i am not discouraging u to get dslr, but dlsr is expensive, hard to use at first time,and u need to invest more..
it is better u to try with prosumer first.. and technologies become cheaper everyday, u can get a better DSLR in future at the same or even lower price.
for good prosumer, try look for canon s5is, or panasonic fz series, they are good too..
http://www.dpreview.com/reviews/sidebyside.asp