I just think that IO became cool and associated with technology so many startups, especially tech associated uses it. I dont think it has any other effect, none is better or worse, depends of the project. I would chose .com for selling tickets but IO for a tech startup 
You're absolutely right. io appeals more to the tech savvy people and ICOs that use them tend to be very techy and wanto to appeal to the tech industry. most tech startups use the .io domain
Most of crypto startup but not sure about all kind of startup were using .io domain.
.io domain is mostly used by crypto related project and i never heard any other based project that used .io domain. it's too rarely
just try to get the more answer for this through internet.
Even paypal has an app on a IO domain, https://www.card.io/, I've even seen political campagins on IO domains, since they are available
i liked https://postach.io/ . there are tons of non crypto IO projects!https://domaintyper.com/top-websites/most-popular-websites-with-io-domain