FWIW, Warby Parker was not the first web-based retailer to undercut traditional eyewear sales, nor are they the cheapest. They do seem to have the best PR, though.
Unfortunately, their range of styles is still very narrow, which is presumably dependent on their manufacturing capabilities.
I have heard of ClearlyContacts.ca (I am Canadian), is Warby Parker comparable?
They basically started a very customer friendly model that other online glasses retailers didn't offer at the time of founding.
EDIT: Basically, customer experience.