Tip of the hat...er here's some more money

There is a clever iPhone app that I downloaded awhile ago called Wedding911. It is supposed to be a place where you can ask questions and get answers from other brides. While waiting for Dan at lunch (he was 10 mins late...hehe ratted you out) I took a look to see if any interesting problems were going on. Well I came across this inquiry about tipping vendors for their services. So here is my dilemma, I understand that tipping is a way of thanking someone and showing approval but I don't understand who deserves a tip. This is something I need help on.

So do you need to tip EVERY person who is doing something? I'm kinda confused here. So the catering staff gets tipped. That is fine by me because essentially we are paying for the food and the tip is for the service of the food, right? The bartender is the same deal, paying for alcohol and then tipping him for the service. Now it gets fishy.

For the photographer we are charged a fee for them to take pictures at our wedding. So do they need to be tipped because in my opinion we are paying the fee that they charge which is for their service (taking photos). We are not paying for any tangible objects like the food, in fact no actual pictures are included and are additional cost (unless you count a proof book). So if we are obligated to tip them (I don't want to be perceived at stingy) are we tipping for the deliverance of a service. This doesn't add up to me.

Same for the DJ, florist, officiant (do not understand this at all), and decorator when does it ever end. A tip on top of a fee for a service that they are directly charging us for.

If that wasn't confusing or overwhelming, how much do you tip? If it is the customary 18% (again I'm not that stingy) does that mean that I need to account for a huge chunk of the budget to be tips. 18% is almost a fifth of the fee and for this I demand to know what is obligatory. For those who had a wedding or planned one I need your advice. I'm not just asking to increase comments on this blog but really need help on this one (email me or something). I'm by no means a cheapskate and want to show people I'm grateful for their participation but can't that be said in a thank you note and not by a transfer of even more money.