Er, no they didn't. Hence the retractions...:erm:
Retractions happen AFTER acceptance by peer-review. It's usually when the papers are discovered by chance, by a 3rd party to be plagiarised/doctored [love this pun]/etc. The authors know very well and take the chance as everyone seems to be mad about quantity in the 'publications' part of your CV rather than quality.
The peer review process is also HIGHLY dependent on the conference. More prestigious conferences will have more prestigious technical programmes (reviewers for the layman). Reviewers are never paid, it's a volunteer job. I'm one for the biggest telecomms conference locally and you'll be surprised at the papers that get submitted. I also do secondary review for flagship international conferences (think GLOBECOM) and the paper quality there is just levels beyond 99% of papers that get submitted to the local conferences.
It's really amazing when you sit down with a paper that has bits copied from other papers by people who can't even follow formatting rules versus a paper where you struggle to find any faults and the only thing you can comment on is how good it is and to try and be very nitpicking with the spelling/grammar.