"Currently solar customers are being subsidized by non-solar customers for these costs (which are in the billions when you include original investment)"

Nope. The solar customer still pays a base hookup fee, including taxes (which support future distribution costs). Here's one (of many) reference: http://www.epa.gov/chp/policies/policies/ututahnetmeteringrules.html

The original cost was a government subsidized program. There was wisdom in doing that on many levels. Not only would they be able to grow the nation faster, but they could also control the quality of the system by creating monopolies. The cost of transmission is a huge barrier to entry...and the law disallows (mostly) competition. Here is a recent distribution cost incentive program worth $3.4 billion from the US Government, as proposed by Obama: http://energy.gov/oe/technology-development/smart-grid/recovery-act-smart-grid-investment-grants