Electrolytics and PCB Routing
My take is that caution applies primarily in situations with power filter capacitors run at mains-like voltages (160/320V bus), but they didn't bother to qualify it. Such caps are typically through-hole. Imagine the capacitor leaking and the board burning..  

The electrolyte could allow more than enough conduction to cause a lot of havoc, but not enough current to cause the fuse to blow. 

I don't think there is much to worry about in a 47uF coupling capacitor... nor even a 6.3V low-Z filter cap on a PC motherboard.



As to your other question.. bipolar electrolytic capacitors are not designed to have AC across them, as the application information indicates. There are some non-polar electrolytics that are designed for AC, for applications such as audio crossover networks.