I see ExAAer's point -- the Saturday stays are basically promotional rates. If I take a free trip offered to me by someone wanting to sell me a timeshare (hi, Hilton!) I can't be shocked when they charge me the full rate after I duck out of the sales pitch.

That having been said, as long as the legacy carriers continue to use completely facetious arguments to justify non-refundable and (especially) non-transferrable tickets, they give up any moral high ground on the subject of fare hijinks.

In short, if they're going to play games with the consumer, they can't be shocked when the consumer plays games with them.