FML IS distributed separately, so you are free to go get it directly.
And like i said, You are free to recompile them for 1.5
And yes, in computer science the rule is to break everything down it its components, but there is computer science, and then there is end user experience.
It has been proven MANY times that the end user cant understand the basic concept of order of installation. Hence the decision to include FML directly into Forge's dist.
So, I repeat, you are free to compile FML/Forge for yourself for 1.5, that's the power of Open Source software!
But we are not going to support it officially. Because it would confuse, scare, frighten, intimidate, bewilder, etc.. the average user for no reason.
PowerPC makes up 0.008% of forge's downloads according to Google analytics.