Under 3.0 and 3.5 rules all attacks can be sneak attacks provided they meet certain prerequisites (I.E. Flat footed or flanked enemy). In fact, if you go here:
http://www.wizards.com/default.asp?x=dnd/rg/20040302a you'll find this little gem:
Quote:
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Provided it is possible for you to make a sneak attack at all, you can make multiple sneak attacks when you use the full attack action. For example, if you have a higher initiative result at the beginning of an encounter, your foe is flat-footed and every attack you make is a sneak attack. The same is true if you flank your foe.
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This is what makes two-weapon fighting rogues very dangerous if they get a sneak attack set up.
If he was running a 3.0 or 3.5 game, that DM was either reading the rules wrong, or was just making it up.