The answers are common to all helos, not just the Robinson, frankly.
The climb limitation for most helos is generally due to the somewhat silly handling requirements of FAR, where the longitudinal stick stability is measured at max climb rate. Some helos have difficulties meeting it, so they impose a climb rate limit at the highest climb rate where the handling is still compliant.
We have Bell lurkers on pprune, wonder what they would tell us?
bladewashout asks a good question. Do we fly as if the engine will quit right now, and fly in every way to completely optimize the response to that failure? Best engine failure protection, for those who would completely slave their flight techniques to minimize the risk of engine failure: Stay Home.
It is a probabilities game we play when we fly, order a steak or pull down our pants. Because we train for engine failure, it becomes THE failure, and we focus on it as if it were the ONLY failure.