Limited Upload To YouTube? "Waiting for WiFi"

Hi guys,
I using Samsung Galaxy S with data plan, it was fast speed.
I'm trying to upload video directly using share from my Phone to YouTube.
I'm only able to upload video below then 3MB other than that it said "Waiting for WiFi" on "My Upload"
I have no problem below 3MB but above that it always said "Waiting for Wifi"
This is wierd...
Why I need WiFi if I already have 3G connection speed?
I don't understand why that so?
In fact Samsung Galaxy S can be Wireless Internet tethering allows to use my phone as a modem to surf the internet on your laptop anywhere, anytime. Or other word I can use my phone as an Internet AP (Access Point) using mobile AP. This allows other devices (maximum 3) to connect to it via Wi-Fi. So it become backbone for my WiFi, so why I need Wifi for? To upload using different AP not through my phone? It doesn't not make any sense. Does anyone aware about this?

Is normal uploading after take video on the camera mode, then click share.
And choose Youtube, it will automatically login to my Youtube account.
And select either public or private and upload. That's it.
When uploading it will bring you to My Upload menu, only files more then 3MB it stuck and said "Waitting for WiFi".