Encouraging people to upgrade? More like encouraging people to upgrade to iOS or Android (not that the latter will get any updates either). The people that are bothered by this are the people that make smartphone recommendations to their friends, don't forget.
This was one of the main selling points of WebOS I think, at least with the techie crowd - fine the OS was new but it would get better and your phone was very likely to be upgraded. It's not surprising that a company like HP don't want to support perpetual free software upgrades but without them I can see people picking other options.