You have to understand, anyone who bought the L version will have convinced themselves it was better. Human nature.
I have Owned and sold both 100 f/2.8's. They are similar in sharpness. The L is pricier and looks nicer and theoretically IS should help... but I never got much blurry pics with the non-L so I did not miss IS.
However if I was hunting for moving insects then the IS would help a little as I panned. Otherwise the non-IS was very sharp too, and add to that, had a wonderful Bokeh.
For wedding, the non-IS is just as good. It depends how much cash you have. the non-IS could probably take 95% shots that the L can, but is 50% the price.
Just for the record I owned both and the L was just a little better with micro-contrast with my copies and the IS can be useful for say flowers without tripods or to help you just manage to get natural light bug pics so long as the bugs are still (you will likely still need to fire off in burst mode and then pick the sharp ones out, but a few sharp ones is better than all but none). (interesting was the lens rental test though which did verify that most L are sharper than most non-L, however it also found that the best non-L were actually a little bit crisper than the worst L copies)
But yeah twice the price is a lot, the sharpness difference is less than say the 70-300 vs 70-300L (although bigger than the 1.4x TC II vs III in the center of the frame, now that one you need 200% view and microscope and careful staring even at that to see the III is sharper, in that cases the difference is more at the edges and in CA) so it may not make sense for a good number of people.
In the end I did like the L better and decided to keep it and sell the non-L, although certainly the non-L is pretty good, but the IS does help at times for me for sure and heck why not get the touch better pop to details and a bit more BG blur when shooting both at f/2.8.