well the key here is that FDEV haven taken a decision on this already in their "skunk work" phase. that very first model of ED they showed to the BBC soooo many moons ago, was based on p2p networking. and it makes a LOT of sense to go that way. specially for a game like ED with very fast moving objects and their relevant positions. all the console games do it, too. so why not ED?
because your testing experience of that p2p in a beta phase isn't very good?! not a very convincing argument. for me the networking aspect of ED has been getting better in every way (stability, lag, no. of human players, no. of NPCs, ghosting etc) since alpha 1.0. and the latest beta 3.03 proves to be nearly faultless even when home on my slowpoke line in rural germany.
here is the link showing the first ever video about ED and its kickstarter campaign. if you have not seen it, well worth a view
there are also a number of reasons that others have mentioned, mainly you cannot change the payment method when you have already sold 150k copies of the game. another is that scalability of p2p is good. when ED is going gamma i would expect that number of players to double and full release, time will tell the numbers. FDEV just needs to call amazon to clusters. i am sure that is possible

and as far as i know they have a new central connections for long-tail content anyways.
and for the record, i would pay anthing via any model to play the game as DB and his crew want to make it. but that decision has been made a long time ago and the decison taken is a wise one ^^