I found two posts from the L&T archives (see below) by The Mysterious H.C. helpful. He said in post 13022 “In Jane Austen's circle of country gentry, showy and elaborate wedding ceremonies were considered rather vulgar” and in post 29972 he had this to say about who would be invited to the ceremony:

Most often, only a few close relatives or very intimate friends would have been invited to the wedding ceremony itself, and if these people weren't already in the immediate vicinity of where the wedding was to be held, then their invitations would have been just some sentences contained in one of the letters that they were habitually exchanging with the bride or groom or the close family of the bride or groom. (If they weren't habitually exchanging letters with the bride or groom or with the immediate family of the bride or groom, then it's unlikely that they would be invited to the actual wedding ceremony in the first place.)

So, based on this I don’t think Mr. Knightley’s absence from Miss Taylor’s wedding ceremony was odd. From their easy conversation and apparent regard for each other in Ch. 5 it seems to be happiness all around between these two. Mr. Knightley does not appear to feel slighted by not attending the ceremony and Mrs. Weston does not appear to feel slighted at his absence. (:D)

I have quoted from these archived L&T posts by The Mysterious H.C. because they both contain spoilers for Emma. (:D) Therefore be warned before reading:

Weddings, engagements, etc... Written by The Mysterious H.C. (August 17, 2000)
http://www.pemberley.com/bin/archives/regarc1.pl?read=13022