I'm glad you brought this up. I too was looking at an Aqua Lung reg at LP. I know that they are not "factory authorized" on many products and have their own warranty. This should be fine on the items I've bought from them including 2 of the same dive computer. However, there is the issue of free parts on the annual service as mentioned above. It is difficult to believe that this would amount to anything close to the 50% savings. You could buy 2 and use one for parts for that much savings!
Not having my own reg and thus not having had to have an annual service, I'd really be interested to know how much the parts cost for this. I can imagine a some o-rings and/or seals but other than that how much could it be?
I would certainly think it would be safer (at least you have their warranty & return policy) than buying on eBay. BTW - LP does also sell on eBay (same prices).
I checked scuba.com & scubatoys.com and neither have Aqua Lung listed on their sites. I would guess that Aqua Lung prohibits online sales. Since scubatoys has a store front you might call them and see if they carry Aqua Lung in the store and if so what sort of deal they can make.
-Mark-