Answer: I’m with you. Your gut feeling on this is actually supported by some of the dialogue found within ABYC standards as they apply to wire runs and cabling in engine room spaces. Basically what the Standard says is that any cable runs over moving machinery need to be secured by metal clamps or clips.
In the photo you sent in, the hoses are actually sitting on the engine, so it doesn’t really illustrate that specific point or potential problem, but the potential trouble does exist in the long run. It’s true, the nylon tie-wraps shown will eventually heat-harden, become quite brittle, and break due the extreme heat they are surely going to be exposed to sitting on top of that engine. Without a doubt, rubber coated metal clips are the best choice for this type of service. Just do a quick web search for metal "P-clamps" and you’ll find lots of sources for the type of clamp preferred for this installation.