I thought if Udina had became councilor in ME1, he wouldn't reinstate your Spectre status in ME2. I think that's what I read somewhere. I do not know this, since I could never bring myself to choose him. How big of a difference this made, I couldn't say. Just looked like a few dialogue wheel choices between, "I'm a Spectre," and "I'm with the Alliance," and "I'm Shepard." when introducing yourself.
But, Anderson resigning to take up arms on Earth was the logical choice for ME3 no matter who was councilor... but to be quite honest... I think Anderson should have promoted Bailey and gave Udina a few more belly punches... you know... for old time's sake.
If people are going to say this just go do that outside of these forums or actually post what it is saying in the codex! Other than that. I do not really care why he came back. I can not even see why you would want some one who is more military in politics placement. Thats just mental.