"As far as I can see the idea that Ofsted has become tougher is a myth propagated by schools that got a decent rating, rested on their laurels and now find themselves with a poor rating."
Agree - though anecdotally there have also been some very quick 'dips into SW / Inadequate' in LEAs with very few / no academies [including one school where the inspector was open enough about it to say 'I have brought with me the pre-written report that puts you into special measures, because of the pressure to have some academies in this county'.
From my observation, in paimaries, what seems to have happened is that schools which have got a satisfactory or below in the past - because more focus was on 'absolute' results, rather than progress, these have often been schools in tricky cuircumstances - have absolutely pulled their fingers out, and in many cases have, after years of working really hard, moved up to 'Good'. (Some, though, with very tricky intakes, haven't, because of the removal of 'contextual' factors in the judgements of progress).
On the other hand, schools that, because of easy intakes, had a record of good Ofsteds based on good 'absolute' results have been caught out. They have not been used to working at full pelt all the time, an element of complacency has been opresent, and the schools have slipped into RI or worse due to lack of progress.
I have moved from a school that pulled itself from Satisfactory to Good (with a very interesting intake) to a nice MC school used to getting 'Good' or above. It has been very interesting - in particular watching the efforts of the leadership team to alert the staff about the level of work, the continuous improvement, the sheer bloody-minded persuit of progress for every pupil bnow needed - something that had becomne 'second nature' to the staff in the more challebnging school because there had never been an opportunity to do anything else IYSWIM.
It therefore measn that a different 'type of school is getting RI or SM - yes, some schools in very difficult circumstances still are, but so are complacent 'middle of the road' schools with decent 'absolute' results, and thus it has become more visible to MN type parents.