So, was granpa's banana more slippery?
Actually, that's a slightly hedged 'yes'.
Grampa's banana had a thicker, more durable skin, in addition to being larger than the bananas we youngun's know so well. The other reason it's so popular as comic relief is because it actually was a real hazard back around 1915-ish. As a 'portable' fruit, they were handy to carry anywhere, and without streetcorner trash cans, the peels got tossed on the sidewalk as often as not. And considering bananas are (and were) the most popular fruit in the US (almost twice as popular as the good ol' apple), it really was a normal hazard. The Boy Scout handbook of 1914 actually listed removing a banana peel from the sidewalk as a 'good deed', it was that common an occurence.
Did you know that the current type of banana everyone eats is called Cavendish because the previously most popular banana Gros Michel went extinct in the 60's?