Incidentally, the rigger's key skillset size is not unreasonable - it's actually in line with the other archetypes. They do benefit from a wide set of skills, though, with the pilot skills, the mechanic skills, hardware, and many other things under Logic being very attractive options for them.
Would you agree they need to go at least skills B? Or do you see it differently?
"Need" is a strong word. They can benefit from it, but as I said, the number of skills they NEED is about the same as that number for everyone else (combat types, who can get away with fewer, and technomancers, who need more, aside). You can make a Rigger work on Skills C, in point of fact, I've done just that; it's all a matter of tradeoffs. With Resources A and Attributes B (plus a couple of 2's paid for with Karma), the character gets very solid dice pools for driving (at Reaction 7, even a pilot skill of 1 can get him 11 dice if he can jump in). At 9, his base B/R pools may not seem great - but he's got the Special Work Area and the Shops to make up for that. Logic 8 also leads to pretty reasonable dice pools for low skills. The result is that the only R6 skill he has is Pilot Ground; even Automatics is only at 1 (the badass cyberarm and implanted smartlink help there, though, putting the actual pool at 12). Had I tried to build this character at Attributes or Resources C, he'd be significantly worse (notably, his rigging-relevant attributes are all chargen maxed - Logic 6 ( 8 ), Reaction 5(7), Willpower 5, and Intuition 5) - hell, as it was I had to give up on a lot of the stuff I wanted to buy at chargen.
If you're really willing to pare things down - if you know what you're willing to sacrifice - you can make even skills C or D work. Part of it is you've got to know what you can afford to have at, say, 1 - and you've got to pay for that with Karma. A bigger part is that when you sacrifice your skill points, you use that to benefit the character in other ways that nicely make up for it.