Short version - when you provide hardware for LMCE, even if you only provide the DVD and instructions on how to install it, but especially when you actually install it as a packaged system - you are selling a licensed, commercial product. Thus you have to purchase a licence for each installation from Pluto, the company that created LMCE originally. Otherwise you are breaking the licence, and with it, the law.
Pluto created a product called PlutoHome - this was a closed source, commercial product. Subsequently, they decided to open source it and share development with a growing community - this became what is known as LMCE. There have been many stages since, but fundamentally, LMCE is at least partly licensed under the PPL as well as a GPL. The PPL placed restrictions on use of the product so that the community/public could use the product freely (in both senses), but that their competitors couldn't just lift their technology and resell it for free and put them out of business.
This isn't really just an inconvenient, unintended after effect of the licensing - in a small way, what you are talking about is becoming a competitor to Pluto by setting up to distribute systems to the public that compete with their solution. They don't mind if you lift the technology and use it personally as much as you like. Its when you start distributing that they have a legitimate concern! Take a look as Fiire, Micasaverde and Convergent Home Technologies - they all have licences to do this, moreover as Hari pointed out, CHT in particular not only offer a complete, supported solution but also are some of the strongest contributors to the community. Any commerical approach to the product that was likely to impact its reputation in the pursuit of profit is very likely very unwelcome. Take a look at the threads about the problems Fiire suffered. I sincerely doubt that you could, currently, support the product as it requires an enormous amount of detailed and specific LMCE technical knowledge.
