IPhone :: 4 32GB Stores 20% + Less Audio Than 3GS 32GB?

It is an undisputed fact that I can store a LOT more audio on my 3.2GB 3GS (on O/S 3.1.3) than I can on my new iPhone 4 32GB. I mean a LOT less - like 20%.

I loaded the EXACT same settings, apps and songs into the iPhone 4 using a 3GS backup. Absolutely no difference. When I tried to syncronize the first time, it loaded the settings fine until it started to copy the songs over. I got an error message saying there was not enough room. I was going to be 3GB short! Yes, I lost 3GB of available audio storage on my iPhone 4 32GB vs 3GS 32GB.

I cancelled this operation and looked at the total "available" capacity of each device. The iPhone 4 was at 29.1GB and the 3GS was at 29.3 - the iPhone 4 obviously reserves slightly more for OS 4, but not significant enough to account for the 3GB less music storage.

I thought the error message might be a fluke, so I loaded my audio in little chunks until I reached capacity, and sure enough, I could load about 20% less songs than in my 3GS.

So what's up here? It makes no sense to me. One thing to note is that I'm using the on-the-fly 128 kbps conversion option (checkbox on the "summary" page when syncing). Since I copied over most songs on my 3GS when I was using iTunes 9.1 and OS 3.1.3, it could be that iTunes 9.2 (maybe in combination with OS 4) has a less efficient conversion routine when converting a 256 kpbs song to 128 kpbs. Or maybe OS 4 is reserving more space per song for some reason.

Has anyone else experienced this? This is a MAJOR deal for me since I already was VERY disappointed that their was no 64GB phone, and now it's even WORSE because I have to unload ANOTHER 20% on my music!