I made a similar mistake visiting S. Africa last year. I booked two separate tickets, for pricing reasons. During the first ticket an agent mentioned I didn't have an entire page free. Admittedly, this was entirely my mistake as I should have checked the rules.

While in a lounge, prior to boarding second ticket where they would be obliged to check, I used the hand dryer in the bathroom to warm my passport and peel off a Cambodian visa filling a whole page. Luckily, neither the lounge agent, nor the agent at my connecting airport, bothered to check.

Upon arrival, the immigration agent mentioned my now "open" page clearly had a visa there before. I said it was cheap glue and fell off, but my operating carrier had said it was ok (a lie). She was clearly nonplussed and consulted her supervisor. After discussing, they let me through, though I was very much under the impression it was a "we can deny you entry, and fill 50 pages of paperwork, or let it slide and get back to our day" situation.

I was told to visit a U.S. consulate while there, to rectify my passport, but declined to do so (I was there only two nights and had vineyard visits etc. planned). Upon leaving the agent didn't even bother a second glance as I had the entry stamp.

Tangential post? Sure. However, it's the operating carrier's responsibility to ensure proper documents. Legally they may be able to pursue you, but that could be very easily fought or avoided. As far as seeking compensation goes... no way jose.