Raven 30,
When did you last ask for total persons on board? We do it for every flight, and it can lead to all sorts of confusion and R/T congestion. Many of those pilots who understand English reasonably well still manage to confuse pax figure with total, leading to further questioning to get the figure we want. Those whose English is a bit dodgy (and there's a fair few of those) will read back any figure that comes into their heads, including QNH, aircraft type, and slot time. It can sometimes take up to half a dozen calls to elicit the required information.