To Tip or to Not Tip-that is the question

Do you ever wonder what the deal is with everyone asking for tips?  I'm at Southwest Florida International Airport right now getting ready to head back to the Chi.  When I was checking my bag via skycap, the worker told me the only difference between him and his Southwest Airlines counterparts inside is that he works for tips.  Okay, so he clearly wanted money for lifting my ridiculously large bag, which I always give, but are you telling me he only works for tips?  Why is this different than checking your bag inside?  In Chicago, I tip because I feel bad for the workers standing outside in Lake-Effect misery, but I don't feel pity for the shorts-wearing workers here standing in 75 degree weather.

It's not just skycaps either, there are tips jars everywhere.  When I got a yogurt parfait this morning at Starbucks, there was a huge jar asking for tips.  When I bought a Carrabba's gift card yesterday, there was a line for a tip on my credit card receipt.  Even when I get a Subway sandwich these days, there is a jar asking for tips.  Should we tip in all those situations? 

Here's my tip: Don't ask the unemployed girl for a little something extra, because you just might find a dirty Kleenex and a chewed up piece of gum in your jar.