I find a company working only with STEP:
http://www.steptools.com/
They use STEP Xml and 9 STEP APs.
They sell STEP libraries:
http://www.steptools.com/products/
Here they talk about AP-214 and AP-203 like standards in solid models.
This is the same in Microstation which only support this 2 APs.
http://www.steptools.com/library/standard/step_1.html
Here all STEP APs in 2004:
http://www.steptools.com/library/standard/step_2.html
Their opinion about the future of STEP:
http://www.steptools.com/library/standard/step_5.html
Regards.