Yes, these benchmarks use forced GC calls (i.e. all phases are STW) because it's the only (good) way I can think of to make theses tests deterministic (maybe you know of a better way? I'd definitely be interested).
Of course, I don't have such calls on production systems; and while concurrent collections greatly reduce the time spent in STW phases, latency spikes are still a very real issue, as I explained here [1]. The monitoring on my production systems leaves absolutly no doubt that those latency spikes are due to garbage collections: once the GC was out of the picture, every thing was flat and fast again.