100 feet is not that low - unusual flight envelopes are what helicopters were designed for - when filming boats, 5 - 10 feet would not be unusual; on powerlines you may be looking at 1 - 3 feet from the lines. You can do it all day long but you have to be on your toes, and obviously if the engine quits you're f**ked.
You're right to assume that you'd be going straight down in that situation - but you can fit into a much smaller place. Personally if i've absolutely GOT to crash into someone's back garden - i'd rather be able to do it at 0 kts than 60kts!
In a helicopter at 100 feet you're much safer going faster - at 120kts in a 44 you can lose the engine and climb 3 or 400 feet in autorotation which gives you a lot more options.