"ground pounding" and "collecting meat"....give the guy a break. I'm not sure what it is about grouse hunters who like to make smarmy remarks about the way others hunt~especially when it's perfectly withing the boundaries of the law and, dare I say, an understandable/effective way to get them when you factor-in how stubborn ruffed grouse can be. (ie, sitting...not moving....even when you want them to sometimes) If you've either shot so many that you only get pleasure from wing shots, then good-for-you. If you have so many where you hunt that you can cherry-pick the ones that flush, then good-for-you AGAIN. If you're like me..and have to drive 3 hours one way, hike all day to find MAYBE 1-2 birds (maybe none)...you can bet your a** I'll shoot one whether it's on a tree branch or flying away from one. I've done both plenty of times now, and I consider both successful hunts. I never regret hunting if I don't find any either, just part of the game.
To the gun question..

Looks like I'm late to the party, but a 20ga. should serve you very well. I've found even modified a bit tight on close birds, so I bought a second barrel for my '68 Wingmaster, had it cut to 22", and shoot it with no choke at all, usually with #7-1/2s. I averaged 2-3 pellets in the breast on every bird I shot this fall~not bad at all. I shot a 12ga. with a modified choke a couple of years ago, all wing shots that year, and it was a bit too hard on the meat. The 20, especially open for thicker bush, has been a great combo for me.
On a side note, my daughter will be 12 this summer, and wants to get her hunter's apprentice license....for the sole purpose of shooting some grouse this coming fall. I've let her shoot my 20, but she's a terrific shot with her Savage Rascal .22lr. Unless she has a change of heart, it will be that gun...on sitting birds..that will define her first hunting experience and I have no issue with that at all. When she gets a bit bigger, I'll take her to the trap range and get her some time behind a shotgun. That will be the time for the wing shooting discussion.