When I started EarthLink's mobile business I actually met with Al and Laura Ries the authors of "The 22 Immutable Laws of Branding". Their advice. Call it EarthLink Wireless.
I have been involved with over 500 startups over the years. I have never seen a sub-branding strategy work for a technology startup. What prompted me to write the article was one of the companies that I am working with (Flux Media) is changing their company name to their product name (Centrafuse) because the use of the two different brands was creating confusion to their potential partners.
YC companies Omnisio, Reddit, Xobni, Scribd, Loopt, Dropbox, Tipjoy, and Justin.tv to name a few all use a master brand strategy. My guess is that nearly all of them do. Perhaps we should ask HN.