Yep, from what I found most of the scores are hacked. Most Flash Games are easily susceptible to hacking, and Diner Dash in particular has a major bug in it that enables people to get the highest possible score easily.
GSN have shown that they don't care about cheating despite numerous complaints, and the Oodles are basically worthless now anyhow, so I don't do anything other than Bingo Blitz.