They wouldn't be downloading two applications, It's only one.
I've seen skin and car mods for this game that are bigger than MTA. The bandiwdth used while playing the game is much more of a significant issue than a single download.
Double standard? I don't know; perhaps he's just not a deep thinker.
I think it's a great idea to combine the two. The two game engines are similar. This allows updates to take effect for both games and people won't complain that MTA:VC runs better than MTA for GTA3.
Also, the people who made the decision to combine the projects are the people who are d