LTNman -
The reason for the council granting full planning permission for the access road, but only outline permission for the development itself is simple, The road will be the core of the development. But each unit will be developed according to the requirements of the end-user, so to seek detailed planning permission would be foolish. The units could be used by companies for headquarters-type offices, or catering units, or training facilities, or hotels, or any of numerous other options, all of which have differing detailed requirements.
Whenever postulating a conspiracy theory, consider that there may be an alternative!
LGS