They definitely aren't "new" as they have sold huge numbers of Xbox and Xbox 360 units, which would make the Surface numbers look pitiful. The molding process for their VaporMag is something that had to be invented. In fact there was no manufacturer that could even do it, and MS had to invest in one. That complex process of production probably has its own unique challenges. Judging demand and not over stocking or under stocking is difficult to do, for any company. Let alone most devices rely on outside companies that build each component, such as RAM, CPU, Touch Screens etc. Any one of those factors could have an effect, something that could be completely out of MS control.
So yes the low levels of stock are frustrating, but it isn't cut and dry like you may think. Even Apple with their huge production investment, buying power, and most likely having a higher priority on components due to volume, can experience problems with stock levels.
And with first hand experience, their service/support has been on par with the industry, as I have had to replace my Surface RT and Touch cover each once. Had no issues doing that and the people were friendly and responsive.