The adapter under normal operating circumstances should never get that hot - mine does heat up a fair amount, but nothing unacceptable and dangerous.
Normal operating circumstances include (as I presume will be in the manual) sufficient ventilation to ensure nothing overheats, the macbook being in a drawer with the adapter sitting on top does not really count as sufficient ventilation. On that count the op has made a mistake, and really has no recourse.
The question does still exist over whether the adapter should be able to heat up enough to cause such damage, even locked away? Does it have any thermal protection or shutoff features should it get too hot that have failed? Or was it just an issue of it working at a correct temperature, but that itself being beyond what the macbook surface was designed to handle?
Only someone knowing the specific workings of the adapter and macbook can really give us a conclusive answer there...