I've wondered if there
is anything the FRG-100B will do that the R-75 won't do?

In my opinion there is nothing the FRG100 can do that the R75 can't, but a few
things the R75 can do that the FRG100 can't.
I looked quite seriously at the FRG100B while shopping around for my current
receiver (Icom R75), and while I liked its looks and some of the programmable
features, and the analog S meter and decent audio, I opted for the R75 for a
number of reasons.
Mainly, the R75 has a numerical keypad to enter frequencies, and the FRG100B
doesn't have this at all, it has to use a third-party wired keypad interface,
which adds to the cost. Not a big hassle but not for *me*.
Also, the R75 has 100 memories, the FRG100 only half that.
I wanted passband tuning to help fight adjacent frequency interference and the
FRG100 lacks that feature as well.
The R75's synch. detector doesn't really work until modified, which is silly,
but at least once it's done it DOES work and the R75 sports that feature. The
FRG100B doesn't.
I also enjoy some lowband VHF monitoring and the R75 covers from 30kHz up to
60MHz, unlike the FRG100B's 50k-30M range.
I still think the FRG100 is a better looking radio out of the box, and I love
analog meters. But no keypad, lack of noise-fighting features and ultimately
greater expense (even without the wired keypad, it still sells for about
$50-$60 more than the R75, and add another $80-$100 for the wired keypad) than
the R75 led me toward the latter.
BUT, the FRG100B has a great many users who are quite pleased with it's
selectivity, efficiency of use when one gets used to programming some of the
features one needs, and mellow audio from the headphones.
For my needs I just couldn't justify getting it, but it's a good radio if your
needs are different.
Linus