Appreciate all the replies folks. As I said, it wasn't a judgement, just a question.
From my point of view, from the other side, I moved out of London to Hitchin, for a 25-30 minute train ride into Kings X. This means we can afford a nice, big three bed house for £300K, have a decent local town with shops, pubs etc. roughly equivalent to anywhere I lived in the past (Balham, Tooting, Herne Hill) and countryside/lovely riding 1km away.
On the flip side, as said above, it potentially restricts my choice of where I work in London and brought with it a £3.5K annual season ticket. I can't commute on my bike, which I loved to do and miss massively, and I have to make that awful decision of last train (a decent 1am) or more beer and an all nighter.
For me the pros outweigh living in W12 or similar (I grew up in Sidcup, so have a built-in dislike for London outside of zone 3-4), but from what I see people post on here, its still a difference of £50K plus more for a similar place 'in London' and you're talking about similar commuting time and combining buses/trains/tubes.