#1 Yes they weigh close to the same weight. I don't have the weight of ancientnoob's coin but the weight is one of the diagnostics used to determine authenticity. #2 There are some really cool tales involving Roman planchets. One great tale has to do with how the Romans learned to treat the planchets before striking them into coins. One treatment depleted the copper on the outer planchet leaving an outter shell on the planchet that was more near to pure silver. Coins struck on these planchets had the proper weight & they looked to be 100% silver (on the outside) but the fundamental planchet core included a fair amount of copper. This trickery allowed the ruler of the day to make some serious profit.
Think I heard this somewhere before. There is a "well-known and regarded" coin restorer in the ancient forum (@YOC) who changes severely corroded ancients to full silvered condition. His "work" is amazing. He may know the "trick" the roman's used. I should guess it involves a torch as heat is something easily available to the Romans.
I believe that the Romans simply heat treated and then pickled the blanks in an acidic solution (maybe urine) prior to striking. This process removed much of the copper from the surfaces of the blanks, leaving them with silver-rich surfaces.
Neat video. (I hope folks here will take a moment to view it). This is the direct link to the video which David Atherton posted in the ancient forum: