The OH and I are in our early 40s, so we're now getting to the 'second round' of weddings in our social circle, after that initial flurry in your late 20s / early 30s when every other bloody weekend from May-August is spent going to a wedding or a baptism or something. 
Anyhoo, we've had a quiet ten years or so, but now we're on Round II and I had forgotten how expensive they are!
Travel, a night's accommodation, gifts etc (plus OH is best man at one of these, so is doing the stag do stuff, too). Three weddings in three months = the better part of £1k.
Now, before anybody accuses me of being po-faced and that 'it's an invitation, not a summons', I bloody LOVE weddings and I am delighted at having been invited to help our friends celebrate: we are both very comfortably off, can easily afford it and I look forward to the whole shebang enormously.
I'm just genuinely baffled by how I managed to pay for this when I was younger, and on a considerably lower income than I am now. 