I had 6 weeks check following c/s: examination, scan and Pap smear. i think smear is very important as one is not one during the pregnancy when hormones go wild. Even if scar is fine, uterus is bact to its prepregnancy size, you need pap smear.
I had two sections, am fairly sure I didn't have the 6 week check the second time as had gone to the UK by that point. Anyway, there was no ultrasound involved; it was pretty much was I ok (yes), check scar (fine), advise me on contraception and do a smear test. Eminently skippable if everything is going well (IMHO) - if you've had a check by the MW and you are not worried about anything, I wouldn't bother.
I also had a C section and I actually believe it is important to have a Dr checkup as there is such trauma to different muscles, including the uterus that probably only an ultrasound would show. Of course if that was part of what your midwife did I suppose it serves the same purpose.