Everything in X-Wing is designed to be balanced at the 100 point level. You cannot arbitrarily change that cap without potentially unbalancing the game with future products.
X-Wing is not Warhammer. The army sizes in Warhammer may change, but so do the individual units and their respective costs. X-Wing is static, so the comparison is a poor one. I sincerely hope nobody is suggesting that FFG should follow in GW's footsteps and start issuing revised costs for all the ships every year.
I agree with the fact that it is designed to be balanced at 100, but I do think going up to 120-125 tends to be okay. Its a matter of how much % change you get and how much more effective focus firing is.
Also, as someone else said, raising the total point cap actually makes a few inefficient things more cost effective as the "wasted" points become a smaller percentage of your list, which you can hopefully make up via synergy or changes to flying that take advantage of the unusual choice you've made.
Still, Tie Advanced are for the courageous.