No, not all. Most notably, video capture and voice activation are not part of the 3.0 OS for the 3G. It does enable many of the other features but some must be hardware supported and video capture is one of them. Regardless it is a very worthwhile upgrade for the new search feature, the cut copy and paste and the added landscape keyboard in MMS and mail alone.
video capture can still be done if its jailbroken. i heard Apple saying that iPhone 2g does not have MMS or Bluetooth due to hardware contraints, but guess what bluetooth file transfer and MMS was already available in iPhone 2g way before they announced this.
i don't think its a hardware contraint whatsoever. i just hope some genius out there knows how to enable Voice Control just like how they enabled MMS for iPhone 2g