We are talking about smartphone screens. There are not lots of flexibilities for UI design. You either slide up or to the side for a lock screen. And what about time?
Sure there are. Android has seen a lot of different lock screen types - drag the small circle out of the big circle, drag the small circle into the big circle, "rotary dial" unlock, pattern unlock, and Samsung's (or was it HTC?) "fling the whole screen" unlock style.
Contextual gesture unlock/launch mechanisms are actually pretty popular. Here's an example with 4 options, but that is by no means the only option set.
The reason for all that creativity is to try and get around Apple's breathtakingly broad patent for unlocking a phone by moving along a "predefined displayed path".
