Basically, its the American Government's way (Bush Administration) of answering to the Atlantic City and Vegas Lobbyists. SOme Governors were paid, as litttle as, $50,000!! to help push the UIGEA 2006 Law through.

An American citizen is able to place a wager on any internet site they want.
However, it depends on the site, who is willing to accept a wager from an American citizen. Thats the catch.
Some internet sites that defy the Law, are sites owned by people (many of which are American citizens), who have no interest in travelling to the USA or its territories. Nor, stand to be extradited to any American jurisdiction, as the country they reside in, will not co-operate with American authorities, as they view the the site owners as, 'they haven't broken any jurisdictional gaming laws within that country they reside in'.
The issue of money transfer, is were it becomes problematic. Once a payment system such as ie; Paypal or Neteller IN THE USA, accepts monies from an American citizen, they must establish the route of the transfer. If it becomes defined that the Merchant Account receiving these monies is of, an Offshore Gaming Site, it must concede and shut down the transfer immediately or face FEDERAL PROSECUTION BY AMERICAN AUTHORITIES.
(LAND OF THE FREE!! LMAO!!)
In final, the American Government wants every American to keep their monies within these boundaries such as Government run faciliites, Indian (Aboriginal Reserves), Atlantic City and Vegas.

Here are two particulars from the UIGEA;
1. It "prohibits gambling businesses from knowingly accepting payments in connection with the participation of another person in a bet or wager that involves the use of the Internet and that is unlawful under any federal or state law."[1] The act specifically excludes fantasy sports, that meet certain requirements, and legal intra-state and inter-tribal gaming. It does not expressly mention state lotteries; nor does it clarify whether inter-state wagering on horse racing is legal.

REpublican's defining moment;
2. The Bush administration had previously adopted the position that it would not finalize any rule subsequent to November 1, 2008.[citation needed] This last-minute rulemaking that binds the hands of an incoming administration is commonly termed the midnight drop.

The final regulations (termed the "Final Rule") were finalized and released November 12, 2008, and came into effect on January 19, 2009, the day before the Obama administration took office.[14] Compliance was not required until December 1, 2009 in order to give the "non-exempt participants" an opportunity to implement the necessary safeguards and procedures.

http://en.wikipedia.org/wiki/UIGEA

If this bill hadn't push through, the Democrats would have nixed the bill, in a heart beat. Now, to get this, Passed Bill into Law, OVERTURNED, you need to go through a ton of red tape and Jesus Christ's blessing.

The only country to stand toe to toe, against the American Goverment and won! dubbed the David v. Goliath, was the tiny islands of Antigua & Barbuda through WTO (World Trade Orgainization). No other country was willing to take on the American Government in this issue. Thats why the American Government, took action and re-modified all their existing Gaming laws and created new ones to reflect the modern day concerns.