I've been thinking: that's how I would design it. That is, I would not have the engine just pull harder and harder, but I'd have it stop at some point. I expect this is a safety feature. I appreciate that you felt unsafe, but yours is not the only way that it can go wrong.
I expect your cruise control cuts out if you put your foot on the brake. But how does it cope with you putting your foot on the gas a bit more? And if you see a steep Hill coming, can you keep the cruise control going by adding some more gas manually (?!)
By the way, do you have automatic or manual transmission? If it's manual, can you do cruise control in a gear that is not top gear?