I think a lot of professionals think in terms of a card becoming corrupt and less to lose on a smaller capacity card. There are also some that think larger capacity cards are less reliable. There was probably a time when that may have been true, but I think it is less so now. Many pros aren't all that tech savvy though, they just want to shoot with tools that do the job.
Let's do a quick timeline here on this subject. Early this century when we were all shooting with 256Mb or 512Mb CF cards, the new HUGE 1Gb cards started shipping. Cautious photographers said, " Oh no...we'll stick with the smaller cards and spread the risk. You can't put all your eggs in one basket". Exactly the same conversation happened on forums when 2Gb, 4Gb, 8Gb etc CF cards started shipping.
Ten years ago I got caught with a too small card on my first job with the 1Ds, a massive 11.4 Mp camera. I've never been caught short again; glad to have a pocket full of fast high quality 32Gb cards. And in 12 years shooting digital, touch wood, I've never had a card failure. All my CF cards get retired after 18 months maximum. They are always top-end Sandisk or Lexar. They're never dropped, and always formatted in camera. They get a deep full format in the computer 2-3 times a year. This all may be complete overkill, but face it, the reliability runs are on the board. Against the possibility of messing up a job or even losing a client, CF cards are cheap.
In this day and age, it's inexcusable for any professional shooter to run short of space at the wrong moment. Part of your professionalism is to anticipate, and up to a point, predict the (near) future.
OP, I'm glad you brought your camera to the wedding. And you got the shot!