I think this whole Delaware thing goes under the heading of "be careful what you wish for".
If Uncle Sam puts a 5% (or whatever, pick a number) tax on all www action do you really think the books are going to absorb that cost? Hell no, it just means they raise the vig. Maybe not the entire 5%, but as much as the market will allow them to get away with.
Might generate an interesting advertising war between books. Whichever advertises the lowest vig increase in an effort to garner as many customers as possible. Also, such a change would draw a lot of amateurs into the market. People who have never gambled before will suddenly become experts if they get lucky on their first NFL weekend, etc.
Regardless, you soon will probably have to lay $115 to win $100. Ten bucks in straight vig and $5 to the Feds. This could really destroy the whole "break even at 52%" theory.
The books will find a way to pass on the cost and blame the government. The players (sick as we all are, LOL) will suck it up and accept it for the most part.
And the thing about making it legal will make it safer - give me a break. It just means the scam artists and phone jockeys will have to cover their paper trail a little differently.
After all, it is called gambling. Now we know why. GL to all.