The rumor was started because the drums are so simplistic on the album. Apparently Nicko was having back problems during the recording sessions so he "phoned it in", but that doesn't make much sense because they went on tour a couple of months later. Also the drums could have been recorded at a later time, they weren't using the live recording style, plus the album was recorded in Steve's own house, so that wouldn't pose much of a bigger expense, there was no studio time to rent.
Another explanation is that he wanted to make room for the guitars, to put them in focus. Doesn't hold much water either.