First thing is that you have to realize that cultural calculations, from what I can see, is a lot like calculating the electric field around some static charges of the same polarity. The charges act as sources for the field, and outside the source, the field is calculated using a reflexive algorithm commonly used in physics.
What this means is that the AI and Player essentially being treated equal in code terms, the sources of this field are the same and have the same strength, in other words, the game is indiscriminate.
There are a few things to note, however. I once played a game against genius setting altarians, and I seemed to be winning. I had half of the planets and some starbases. However, within weeks, the altarians won because they churned out this incredible amount of influence. I was perplexed and desperatly wanted to find out how this could have happened. So I loaded the savegame in cheat mode, gave myself loads of cash and spent it on espionage to discover their planets, bonusses, etc. Also revealed the map. Turns out they conqueored 2 influence starbases, and quickly upgraded them ultimately tripling the strength of their cultural sources. No wonder.
So there is no magic or faul play, or bugs, from what I can tell it seems the Ai wins fair and squar.