Not sure the poll is reliable.
Most answers are based on what players remember, not stats they carefuly stored <- 1 bias
In my case, where I have some stats (not complete though), it shows nothing of value in terms of conclusions (not enough values, not enough delta between values to exlude mere chance). The invite I've received the most is one that people voting received the less.
It does not mean that the probability of getting any invite is equal among all brands, but IMHO it does not allow to conclude the opposite with certainty.
And having one or two accounts won't change much,you'd need many more people with sound stats to maybe show something is wrong. And you could be "lucky" with a sample that supports your conclusion but that is in reality non-representative.
Here only 35 people answered. Maybe a lot of people did not open the thread because the title implying that some invitations are received more frequently than others, do not apply to their experience <- 1 other bias due to the title
35 among the people present on GTPlanet is very few, and among all players in the world, is asbolutely negligible.