It's getting kind of late in the season for hydrangea blooms, are you sure it's not just the normal flowers dying back? This is big time spider season, late summer, and I've never heard of spiders eating or bothering plants (they're carnivores), so I don't think your spider webs are the problem. Around the mid Atlantic / northeast, this was a terrible year for all the hybrid variety hydrangeas; the plants look healthy but barely bloomed. You're fortunate to have such profuse blooms this year! It's hard for me to tell from pics and I'm no botanist for sure, but as a plain old homeowner with hydrangeas I'd say they look normal.

Depends where you live. It's the season for hydrangeas here, not too late, they bloom into October. It's been very dry here and they need lots of water, that could be the reason for the brown.

No blooms at all on ours this summer as of yet, despite healthy leaf growth. Seems to be the norm for my part of the country (CT) this year.

Yes. We even asked an expert at the NY Botanical Garden about it. She said this season was bad for hybrid hydrangeas, but it has been a banner year for native (oak leaf) hydrangeas.