Nope,
The story I heard was that the taxman tried to get extra money out of them as they classified it as a chocolate biscuit, which has higher VAT (or something) than just a biscuit. Cakes have an even lower level of this tax.
It all went to court and jaffa made an extra large version to show that it was a cake.
I think the acid test is that when they go stale a cake goes hard and a biscuit goes soft.
However I could be wrong and just made that all up.
ETA: Beaten by Chris.
