Oh Nicola don't think it's anything to do with that! It's her view based on the type of kid Z is and that a lot of kids start waking again, getting out etc when moved to a bed...I think it's their (plunkets) view that toddlers like structure/routine etc so minimal change during that developmental period makes for less challenges to mum and dad lol. She just said keep him in as long as possible unless he climbs out or doesn't fit.
Also, remember we have T as well, waking in the night etc. which is a factor too. She knows ME as well, so maybe that was a factor.