It's certainly a bit more of a pain if you're paying with card. As noted in a sibling comment, it's pretty uncommon for bars to allow you to run up a tab in a lot of places in Europe. I lived in Sweden for awhile recently and out of the many bars I went to I could only think of one or two in the entire nation that allowed me to open a tab. So you have to do the whole song and dance with typing in extra every time you go to the bar (assuming the card machine is set to allow it, some aren't). There isn't even a guarantee that the extra amount will go to the bartender, so your best bet is to just tip in cash. But wait! a lot of bars in Sweden for example don't even accept cash.

My point being that it is out of the norm to tip for drinks in a bar.