Can you see a reference to them charging VAT? If not, that's pretty ludicrous.
http://en.wikipedia.org/wiki/Dormant_Commerce_Clause
"The central rationale for the rule against discrimination is to prohibit state or municipal laws whose object is local economic protectionism, laws that would excite those jealousies and retaliatory measures the Constitution was designed to prevent"
I was under the impression it's a legal requirement to show the inc VAT price. (And, show it as the most-prominent price -- no trickery like showing exc VAT bold, and inc VAT in fine print.)
http://www.jetbrains.com/idea/buy/choose_edition.jsp?license...