Online Gambling Not Banned Yet
For the moment, the rush to legislate the ban on online gambling has been slowed. Senator John Warner, (R) from Virginia, has refused to allow a ban on online gambling to be tacked onto an upcoming defense bill. Opponents of online gambling were hoping to tack their measure on to a "must pass" bill but will apparently be forced to delay. Congress recesses in one week, giving only a few days left if this measure is to be passed before the November 7th elections.
Ultimately, I'd argue that its an ineffective band-aid on the cancerous sore that is our winner-take-all legislative system. We desperately need to have proportional represention. Like, you know, every free nation on Earth. But the powers that be are too entrenched in the two party system.
To answer some of your questions... (I work somewhere on the Hill).
Senators or at least the few that I know or have come in contact with, usually have some sort of philosophy that they follow. This philosophy or set of beliefs serves as a guide on how they will vote. Occasionally you will get someone that is easily influenced by newspapers or political lobbies, but that is in all actuallity, not as common as most people think (which is why when it happens it's big news). There are very strict rules about what kind of gifts politicians and their staff (Senate Staff is limited to 50$ for gifts at receptions) can accept and what they can't.
For the most part, legislation is not written by Senators (Rep's may write their own). Usually there is a Legislative Assistant(s) or Legislative Director in the office that will write the actual bill or ammendment. The Senator will then review it, and if he / she approves it - it will be submitted to where ever it needs to go (usually a committee of sorts). Often they are attached to other bills, since the legislative process is very slow (and attaching it to something may speed it up).
Now, as it is election time, many people that are up for re-election are submitting all sorts of things. However, they aren't trying that hard to have them get passed (thankfully - or I'd have no free time), just submitting them so they can claim to have done some work on a certain issue that they may feel their constituents care about (or more likely matches their ideas). Lame Duck session in December, is when the outgoing folks actually sit down and try to get this crap passed.
So you can assume, that this bill was introduced by someone that believes gambling is wrong. It has nothing to do with the mail that they get, the phone calls people make or the faxes that come in. They don't even see most of those - interns and other staff handle them (although a few Senators actually read a sampling of handwritten mail each week). The politician usually gets a report each week of what mail came in, what issues were popular and what was the stance of the mail (for or against). Usually batch letters (meaning large bunches of faxes / letters / postcards that are all the same ) are not included in that count (cause people often send them in without actually reading them or knowing much about the issue, and mail from someone other then a constituent (meaning outside the politicians district - exceptions being the VA and Natural Resources Committees) or someone that did not put a real mailing address (like the people that always sign with their email address) is ignored. In the event that the politican does not have an opinion on something yet, this mail report will serve to influence their opinion in addition to the research and hearings that they or their staff will conduct. However, their opinion is usually in line with their established philosophy. Long story short, this ammendment was simply so someone could satisfy a mark on their philosophy checklist (most likely), and that is why it was rejected by the Senator (who dislikes this sort of stuff) and not because of some lobbying group.
The best way to stop these things, is to either write large amounts of handwritten mail to your senator / rep (not other peoples), or simply vote them out during elections time. Problem is -- most people aren't informed enough to actually know what's going on (or at least that is what I see from DC). It's easiest to contact your Senator / Rep at a state office also (if they have some), since most of them spend weekends and when session is out at home.
There is always a frontier where there is an open and willing mind