I seriously doubt that. I only have global sales number, not US specific, but there are many online retailers that are larger. Newegg had around $2.7 billion in revenue in 2013. The same year Amazon had $68 billion, Apple had $18 billion, Staples and Walmart both had around $10 billion in online sales. Sears (a company that every talks about as dieing) and QVC (yes the website for that crappy home marketing TV station) both had nearly $5 billion in revenue. Even among consumer electronics CDW and Best Buy had more online sales at over $3 billion each. And again, while these are global numbers, most of those companies are US based, with strong US sales.
Newegg is one of hundreds of online retailers of simular size. While it is a great company, it's adoption of bitcoin is by no means an indication that something has gone mainstream.