There are plenty of horror stories of Paypal holding funds. They've been doing it for far longer than most these other companies, since they've been around longer than most of them.
I have been using Paypal for 5 years for my startup and I don't have any major problems with Paypal. Sometimes, customers filed a case agaist us and Paypal decided that the case was closed in customer's favor although we did nothing wrong. However, it's very rare.
All it takes is a few quick searches from the search bar at the bottom of the page to see what I'm referring to. You can search just "paypal" or "paypal stole" or "paypal froze" for some of the more egregious examples submitted to HN, or "paypal banned" for some of the more common ones of paypal reclassifying businesses after years of working just fine.
Much of them are older, because honestly Paypal had quite a few years of being the vendor of choice before a lot of alternatives came around. I'm not sure if that means Paypal had enough competition that they had to deal with their behavior or they're just used less so you hear about the problems less, but for anyone that's been around for a while, hearing about Paypal screwing someone over is not going to sound like something extraordinary.