Actually, the 17 grain is a frangible round, but the 20 grain is a "controlled expansion" round, and is far less prone to breaking up at the slightest hint of hitting anything. The lack of ricochet is over stated IMHO, the 17 DOES ricochet, and so you shouldn't be taking shots where a ricochet is likely to cause a problem. This is the same for any rifle IMHO. I wouldn't take a shot with the .17 that I wouldn't take with the .22 because of the ricochet danger, so the supposed gain just isn't there.
As always, that's just my opinion.
Matt, personally I agree, but I was giving a widely