For me the simple reason why they did release a lot of average games with a gem inbetween is the following.
You create the VC service and want people to buy as many different games as possible. If you give them everything at the same time. They will buy the games they KNOW are good and thats it.
If you make the good games RARE people are more willing to spend their money on less known games.
its a bit like the 3ds launch. Dont give them really good Nintendo games, so people will likely try out something else. And they did. It was not uber successful but to an extend it worked.
For me the bigger Issue with the VC is the crappy quality of the games (slow 50hz games, black borders, sound stuttering with sega games, pal games forcing you to use 576i instead of 480p etc.etc.etc.)
and the high price for really old games especially in europe.
