I think virtual pets are just inherently feminine.
"Dude, my super-tough pitbull is totally tussling on a piece of rope!" ...exclaimed a chubby guy who was busily poking a touchscreen with a little magic wand stylus.
They'd have to change the name, too. Something that sounds good with "bro" after it, becuase "Just kickin' it, playin' some Nintendogs, bro" sounds gay.
How about:
Hyperagressive Throatcrushers XXX: Bulldogs & Rabid Dobermans
Use Puppies To Get Ladies (Then Touch Their Waz With Your Wand) DS
If You Look At Him, He Bites
I'm Not Sure This Is A Dog, I Found It In The Woods Wrestling A Bear