I never heard of it until my 3rd child. With my first she definitely had one and it was my mother's cue to up her 'that child should be on solids stance'. DD2 never had a sleep regression didn't start solids until 6 months showing my mother was talking rubbish and ds had the most blatant 4 month sleep regression ever, he did not start solids for 6 months either.
My dd did she hadn't been sleeping through previously but had been in a pretty predictable routine, for 2 weeks around the 4 month mark she was waking multiple times a night then getting up for the day at 4am but it did settle back down and she started to sleep right through from 5 and a half months.
The thing about MN is that people only post about bad things. I have spent the past three years on here terrified of sleep regression, fussy eating and insane tantrums. So far none of them have arrived. DD has always liked to sleep, and still does, touch wood.