First couple years? For those of you that have been paying attention, B and D Prepared have been around a while. That turned into STU and STO, which has been around a couple years. The only new thing is STL, which is a 'sterilized' version of STU.
And yes, the STAC has been changing rules that have drastically affected competitors. 2009-2010 rules state "Any engine from the manufacturer". Woohoo! Nissan can finally compete! We're not stuck using a cast iron truck engine that costs $15,000 to build and lasts 3 races on a set of bearings.

oh wait.. now here come the 2011 rules where "Only North American" engines are allowed. Nissan hasn't sold a GOOD RWD sub-3L engine in the states in decades. I personally know of 3 people who were building cars with the SR20 in them that can't race due to the rule change.

STU also 'lost' 2" of chord length on their rear wings with the 2011 rules. APR makes a special version of their GTC-200 specifically for the class. IT's 48" wide with a chord length of 8.75". 2010 rules were 48" x 10.5". 2011 Rules are 48.25" x 8.5". There goes another $1000 I've invested into the class that I have to try and sell on ebay at a loss. Not to mention manufacturers like APR that made an investment to build a part they can't sell now.