Lem and Crowley are very different people and have far more different relationships with Vic and Shane. They've known Lem a heck of a lot longer than they've known Crowley. Crowley was given the opportunity to give up Vic to benefit himself and took it right away, while Lem continually protected Vic and the team and even chose to hurt himself in order to protect them. Plus, Shane had a vendetta against Lem back in Season 3 and 4 and so he probably still secretly hated Lem.
The point is that Shane should have trusted Lem and not used Vic's actions against Crowley as a tent pole because they're totally different situations with totally different people and possibly similar consequences. Shane is a piece of crap and he deserves to be in the grave instead of Lem. I might be able to settle for Vic pulling the trigger on Shane later in the season, but something tells me that won't happen even though Shane deserves it.
Burn in hell with the likes of Guardo and Armadeo, Shane Vandrell.