Yup, they do different jobs entirely.
A discovery scanner finds stuff, and lets you do a 'basic' scan (type and name).
There are three types as mentioned above, but the only difference between them is range.
I say 'only' but that's pretty major...an advanced scanner will find EVERYTHING in the system with one blast of the foghorn from wherever you drop into the system, whereas the basic one only scans out to 500Ls, which is pretty crap!
The surface scanner does an 'advanced' scan, and this nets you more creds when you sell the data, and I believe it's the necessary scan for 'discovered by' status, although I could be wrong on this last point.
So, to maximise exploration, you need both a discovery scanner and a detailed surface scanner.
/ninja'd - why does everyone type quicker than me
