Most stores (Rendo, Daz, Poser Pros, RDNA) require the object to be separated from the prop and referenced. There are many numerous benefits to this, but the main one is to make supporting add on products easier.

For instance, how do you load an object into a 3d paint application, if it's imbedded in a prop file? Or how do you load a 3d object into uv mapper or photoshop cs3 to check for seams for a new texture?

MANY reasons why it's required, and I wouldn;t even dream of buying something that didn;t have objs ripped.

Just another one of those developement details that increases the work for developers, but also increases the useability to end users.

Way too many people take way too many things way too seriously.