he said "early" not "earlier"

... beside, I'd assume until they are ready to talk about the "other methods" of acquiring that early access we will not know for sure. Even if, then I doubt it will be significant.
If the Demo is available sometimes in January (at worst 31st) that will still leave you with over a month of trying the MP part of the Demo out

. Which should be fine in regards to seeing how it plays. Also I'd assume that Bioware might want some feedback on balancing of classes and levels, server stress tests, free word of mouth adverts from the "demo players" etc. so I'd say that Bioware want to get as many into MP as possible ... which is just possible with a wider range of options.
So getting people interested in competitive MP (Specifically BF3 as there you'd get the best out of the game by actually playing as a squad on not as single players) they should get good feedback on how the MP part of ME3 is .... which just can be good for them Bioware

.