Special mention to the non-attenders

Its best not to mention anything about no one being there since they can't make it to your wedding. Be grateful to those guests there at the wedding and reception and say for those in heaven. That should be sufficient.

Ditto this! If they can't come, it's unfortunate but not something that needs to be mentioned.

I don't think you need to do anything... unless you've done some destination wedding where many of your close family and friends aren't able to attend.

You don't really thank people for not attending your wedding... haha.

Personally I wouldn't be mentioning those who didn't attend... just like how they won't be getting a thank you card (unless they were to send us a card of course).

My sister did this for her wedding as it was in Australia and not many family members could make it due to the expense.
She had my uncle gather small messages from couples, or families that were not able to attend and read those. Gave it a little bit more of a personal touch from each family that couldn't attend