Yup.
The most probable reason for this is compression: when you rip a DVD, you obtain a video file that is compressed and is, thus, of more or less worse quality than the original.
Especially if you think that the quality of DVD videos (plus special features) takes up around 4GB of disk space and that the videos you find in P2P rarely go over 900MB

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

"Raise your can of Beer on high
And seal your fate forever
Our best years have passed us by
The Golden Age Of Leather"
-Blue Öyster Cult-