i have used acrylic sheets for years, smudges and such come right off of them easily. the polycarb can scratch easily but is super strong.
i also have some classic arcade tinted glass, it has been used in a cabinet in a commercial arcade for 15 years, was taken out of the cab and placed into storage for 10 years, it looks great.
i get the feeling this guy wants you to special order some expencive piece, and thinks he can get away with it because you asked for such a thin piece of acrylic. (he assumes you know nothing about what your trying to do, and thinks he can make a quick buck) i assume he suggested Macrolon or Marcoclear as the sufficent replacement as that is the only clear hardy plastic i know that starts with MA. if this is what he suggested do not deal with him. Macrolon is a brand name of polycarbonate much like Lexan. this means he is trying to sell you something that is more because it sounds cool.
my suggestion, go with a 25-45% (grey or black) tinted acrylic 1/4 at the thickest 1/8 at the thinnest for the cover, 1/8 is the thinnest i have seen acrylic, he was right in that the 1/16th would not hold its own. he said own weight, what he wanted to say was suface tension is not sufficent to provide solid status.
EDIT: in rereading your post i figured i would do a little inform here. Plexiglass is a brand of acrylic, so is lucite, much to the same effect that klennex is a brand of facial tissue and kraft dinner is a brand of macaroni and cheese.
EDIT #2: because i cant let things go, i went and found the website for the guy that i use sometimes, the website actually has a 1.5mm thick acrylic sheet... that means it is actually slightly skinnier than a 1/16th sheet. He has it listed as ACRYLITE FF SHEET so new tech might have made it possible... i want to see this stuff now...