Mobile handset companies are notorious for abandoning their existing products as soon as it's been launched. They actually have no interest in maintaining their existing products (I have a Samsung Omnia II that never got a single update since it was released in late 2009 on Bell Mobility). Instead, they launch new handsets with the latest OS that you have to buy - after your existing 2-3 year contract runs out, of course. Hence the popularity of custom ROMs on handsets as that's their only option.

The eDGe is a different sort of beast as it's a mobile internet device as opposed to a mobile phone, and enTourage isn't an <insert expletive here> phone company.