Charging issues on iPhone4

This is maybe a little technical question.
I hve been using one USB port from my monitor to charge and transfer data on my iPhone 3Gs without any problem. I even used the cable (USB to 30 pin, not official Apple) via an USB hub connected to the sme monitor USB port. Still no problem (both charging and data).

Then today I happend to connect an iPhone 4 (or 4s, I am not sure) to the same cable (both straight from the monitor USB port or via the hub) and to my surprise the iPhone did not charge (and no data exchange of course): as if nothing was connected!

Did Apple changed the D+/D- codification from 3Gs to 4/4s?

Should not the USB port automatically adapt and at least charge at a minimum current?

Or is it a too high intrinsic resistance of the cable?

Both iPhones are original products. Only the USB --> 30 pin is not original Apple (with original cable, no problem to charge or transfer data from the omnitor).

I hope someone has some feedback!
I am so curious right now to understand the problem! :confused:

Thanks in advance!