In other words, this site is pretty safe...
Sometime it is easier to download from the web than to look into the CD box. The main issue with downloading is that most likely the DVD is not the original and has been tweaked or customized.
The best way to know if the DVD is an original copy is to look at the MD5 checksum.
So here we are starting a list:
|snow leopard retail 29$||817F2D9CFB56885D6E8E3FD99855B691|
|Mac OS X Install DVD.dmg||a98ed4f5b730f384cca66ae026974009|