When I bought my house, the laurel hedge was not being pruned (it was more than 2m thick), but there was no evidence of flowering: it took me 8 months to close the deal, and it was some time before I addressed it, so I had a whole season to observe it. I've seen some other people's pruned/shaped laurel hedges in flower. So I think that there are some that never flower, some that always flower, and some that only flower if you don't prune them. Both P. lusitanica and P. laurocerasus are used for hedging, and I think the latter is the strong flowerer. Also there are many cultivars of the latter, and maybe some are sterile.