I think Tracy Cox later clarified in that blog post that the questioner had indicated that there were no underlying problems, she was just being lazy and wanted Tracy to back her up.....a lot of people gave the suggestion that people in relationships owe each other some kind of effort and it's not unreasonable to request it - demanding is of course a different thing.
My opinion is that sex is as valid a request as asking your partner for a cuddle. As a partner you can deny the request - but persistant denial on one persons part may lead to feelings of neglect and the break down of the relationship.
Ax