Okay you can't compare the two and what's wrong with Roblox aside from the people involved with it?
big rigs has no community of any sort and roblox just fails there, the roblox community consists all immature and privileged children and the mods have no clue how to run a community and are cash whores
big rigs has awful gameplay, with no physics, where as roblox has very nice gameplay, i always thought it was interesting and very fun to build in it, not to mention the awesome physics
big rigs has moderate graphics, not horrible but not very good, they could be worse and roblox has decent graphics at least