http://www.cisco.com/en/US/prod/collateral/vpndevc/ps6032/ps6094/ps6120/qa_c67-700608.html
From the FAQ IPS is included in the base hardware (does require a license) with dedicated hardware on the 5545 and 5555 models. The module slot is for I/O only now although I'm not sure how the 5585 fits in there. Not sure on how feature set stacks up compared to the older IPS module, hopefully someone will speak up on that.
Other helpful info on the new ASA's:
http://www.cisco.com/en/US/prod/collateral/vpndevc/ps6032/ps6094/ps6120/qa_c67-700607.html
**EDIT** Woops, my bad on the "dedicated hardware IPS" info above, what I was looking at were the dual power supply support specs. The 5545 and 5555 both support that. Hardware IPS is built into all new ASA models hence the exclusion of a physical add-on module for that.