Oddities: 1) Number of results are different 2) First 20 results are different 3) Click to page two of Regular Search results – the number of results jump from 11.1M to 11.8M and results 21 and above exactly match Advanced Search.
Because of this phenomenon (particularly #3) several top 20 Advanced Search listings don't show up in a “Regular” Search.
I checked it out and saw the same discrepancies as you. It seems that the advanced match is an exact replica of Google serps and the regular has some extra stuff. I matched it to inktomi but didn't find anything definitive.
Any ideas why this could be happening? I hadn't seen this before and have to do more research.