Yes, this is very common. Often, much of the fee is actually to cover the cost of shooting the event and it is unfortunately relatively common for people to decide after an event that they don't care to get photos after all. You can find photographers who will charge a smaller sitting fee (the cost of actually shooting the event) and then more for each photo you want a copy of, but it's generally easier and cheaper (for both) to offer a bundle that includes everything and the cost of that is typically due at the time of the event.

The reason a photographer can offer the bundle is that it is guaranteed money for their time. Sitting fees are generally not enough for a photographer to get by on alone, so they have to sell images as well. Doing a bundle means the customer takes a risk that the images might not be as good as they would like, but it also means the photographer sells the images much more cheaply because the customer chooses to trust them.

When doing sitting fee only, the photographer may not sell a single photo, so they have to charge more for each photo that they do sell to make sure they still make enough money from the job. This almost always ends up being more expensive for the customer (at least if the photographer is any good) since the photographer is taking all the risk.

If you are uncomfortable paying for everything up front, you could ask if they offer an option to separate the sitting fee and the image fees, but that is generally (much) more expensive as there is no guaranteed income beyond the sitting fee. The image fees would be paid on delivery of the images under that kind of a setup though. (The sitting fee would still be due at the time of the event.)

As to making exceptions for a company that is going to be reliable, you really don't know who is and isn't reliable and you run in to problems if you vary your policies from one customer to another. I've been ripped off by national companies with TV deals that decided not to pay for service (they actually canceled the check they had already given) because of mistakes made because they didn't fully disclose details that I had asked for. Bad experiences dictate caution and it's just too messy to make exceptions for people you trust since then people get upset that you don't trust them enough to give them the same exception.