It is because, these accessories used to charge the iPhone through the firewire pinouts in the dock connection. The new iPhone only accepts charging via the USB pins.

Try an accessory like this:

http://www.cablejive.com/iphone_3g_charge_converter.html

Here is some good reading too

http://www.informationweek.com/news/personal_tech/iphone/showArticle.jhtml?articleID=209000104