Yes, I'm sure oversized played a significant part in their choice of race, but Str/Con and Str/Dex are pretty attractive for melee fighters too. When Hrav was created, Bugbears were the only Str/Dex race available. All of the minotaurs were created before PHB2, so it was either minotaur or warforged for Str/Con, and I get the feeling that warforged are an acquired taste.
Pretty much that right there for Grim. The bonus to stealth was nice for a ranger, too, especially for one with a "scout" backstory like Grim.