As an American, you can get all or part of the $3,000 back if you file for a tax return with the IRS and all of your receipts are sent with it. At least, you will only end up being taxed 30% on your net profit. Americans are also able to make deductions on losses and other expenses related to their poker playing.
For many European citizens it's a lot worse. If you are a European citizen, you will in most cases get taxed by the laws of your specific country. This often translates to paying taxes on all of your gross winnings with no chance of deducting anything at all! Not the net profit for specific tournament winnings, not any kind of losses, or hotel expenses.
Also, first you have to get by the American IRS, and to do that you will need something called an ITIN number (Individual Taxpayer Identification Number). If you have this number, then the Rio won't hold the 30% themselves but they'll leave all the paper work to you and the government that ends up taxing you. (Preferably, poker players should be Canadian or British as they don't have to pay taxes on gambling winnings.) This number was once easier to get but the IRS has tightened their policies since 9/11 and doesn't give it out as freely anymore.
As a European citizen, how do you get an ITIN number? In order to get the number, you have to have a legitimate reason; this means that you can't apply or receive it until you actually have a tax return to claim (i.e., you have to win something first). If you cash in this year's WSOP, you can apply for it in January 2006, at the earliest, and hopefully you will get the 30% back sometime in 2006. During this time, you'll have to hope that your own government doesn't tax you again before you have received your tax returns from the IRS.
Do all American players pay taxes on their winnings? No. Many poker players have 'backers' (people who stake players for all or part of their poker tournament profits), who do the paper work for them and are also responsible for paying the taxes, just like in any kind of business. If you have a backer or someone who is willing to sign for your winnings saying that they own 100% of your winnings, then your problem is solved. Obviously this system is widely abused by many players. For example, if your 'backer' happens to be Canadian or British (and a holder of an ITIN-number), then both of you are pretty much in the green, literally