The press release avoids the word "hack," but Sputnik isn't working with Linksys, just its routers: The Linksys WRT54G is one of the bestselling routers in the world, and its firmware uses software that comes with a variety of open-source and free software licensing requirements for publishing changes. Thus, there are many projects which hack the Linksys, turning its inexpensive hardware into powerful components of larger systems, like mesh networks. (Switched WLAN is more difficult as Linksys uses Broadcom chips, which do not have open-source but only binary distributions.)
By using a commodity AP, which has always been Sputnik's plan, they allow powerful centralized network management and monitoring through their applications, and that's where they insert value and extract revenue. The AP cost becomes so low that's its efficient to deploy more of them since management time and expense doesn't grow per AP.
Sputnik's Agent software works on the Linksys WRT54G and WRT54GS. Read the press release.