Why does Rudy Project dominate the aero helmet for triathletes?

Because they used to give their helmets away for free to all Kona athletes who signed up.  Basically the athlete agrees to wear the helmet for the next year in all races, but it's just honor system.  Nowadays there is a cost for Kona athletes, but I think they get a helmet and sunglasses for like $100 or something.  A super good deal for the athlete, but that's the marketing price Rudy Project is willing to pay to advertise as the #1 helmet in Kona.

Exactly, they more or less give them away at Kona to get those numbers high.  Then they put a MSRP of $350 on their website but you can get 40-50% off coupons all over the place so people see them being used all over the place then think they are getting a great deal with the coupon and boom, lots of sales!  Seems to be a very effective marketing strategy on their part!

The Wingspan also aero tests really well (at least it did for me).  I didn't end up buying it because I got a good deal on an LG P-09, which also tested well for me.  As Arend mentioned, you can find 40-50% off discount codes fairly easily (USAT has one if you're a member), which makes it an inexpensive, good helmet.

They're the Xterra of helmets

Kona used to be a great benchmark for the industry, but if you've ever been there that week, you can see how companies are skewing the numbers by giving it away (to some degree. others reward you for using..aka bike companies giving swag to people racing their brand).

ummm....what?  please provide some proof for the bold....  what I understand is that they are rarely the best helmet for a person, but are always one of the best, if you can't afford testing seems like a reasonable way to go in my book.