In terms of databases, what does 'roach motel' mean?
Generally, I understand (could be wrong of course) it to be either


opaque vendor lock-in
difficulty in re-using data how you want


The second point is seen every day

You buy an app that runs on a mainstream RDBMS: you can report on data, extract it, mine it whatever. Or you buy an app that locks the data into some internal, opaque, proprietary format (not a well known one like PDF or DOC or XLS) where you are forced to use the vendor's (perhaps limited) API.

A couple of other examples


Larry Ellison on Salesforce
Facebook vs Twitter