a couple of thoughts here.
one, the US also has (AFAIK) a lasse fair economy throughout the entire game. What I think that most everyone is missing here is that this is one of the REASONS for immigration to the US, not a hinderance to it. the US is not saddled with a landed aristocracy as europe is, and therefore doesnt require all thoes silly social reforms (at least till the great depression. IMHO one of the reasons for the gap in time btween VIC and HoI, incidentally...)
The 'hardcoding' of immigration just being higher to the US, while i think its a bit of a cop out, is not really a BAD route to go. after all, the US epitomizes everything that european (and slightly later, Asian) emmigrants desire. Not the last factor is that the US government actually encuraged immigration. Cheep land that is available to anyone with means to get it. true religious freedom unlike anywhere else in the world. and simply an accumulation of WEALTH, which anyone can get at... or put more simply, the American Dream.
yea, all that is a cleche'. In terms of social programs, we know better know. however, we are 21st century people. you have to attempt to think like someone of the period to get in the right mindframe...
as for Texas. first, your in a war with mexaco. even when your not in a hot war, yout seriously threatened by mexaco. second, unless you hold corpus christi, theres no coastal provences. even if you do hold corpus, thats an extremely small shore, and quite a bit of extra distance to travel. third, Texas is a western area. the west doesnt get immigants until at least the 1870's. this is true historically, and from what i've seen thats what heppens in the game as well.
anyway, hope I didnt ramble too much...