Same .ai files, but there's more then 6 times size difference!

[Vintano]

Does anyone know how this happens? I've received them both on a client's CD and it doesn't bother me, but I'm just curious
What can be so large in the 623.4 KB file?

[Albacore]

When you sav AI file you have the opportunity in the Save box to make a compatable PDF file as well and this creates the larger files size. This was a great moan when AI CS first came out by users untill they realised that all you had to do was uncheck the ticked box.