OK, I'll bite, you made me curious, so here is what I found:
According to the Oxford English Dictionary, the “grandfather” clock was invented in the mid-1600s but at the time was called a long case clock due to the tall case containing the needed long pendulum and weights for an 8-day clock.
A song by Henry Clay Work in 1876, called My Grandfather’s Clock (referring to a long case clock), told from a grandson's point of view, is about his grandfather's clock. The clock is purchased on the morning of his grandfather's birth and works perfectly for ninety years, requiring only that it be wound at the end of each week. Yet the clock seems to eerily know the good and bad events in the grandfather's life – it rings 24 chimes when the grandfather brings his bride into his house, and near his death it rings an eerie alarm, which the family recognizes to mean that the grandfather is near death and gathers by his bed. After the grandfather dies, the clock suddenly stops, and never works again.
The Oxford English Dictionary says that this song is responsible for the fact that a long case clock is also called a "grandfather clock".