@mylogic - they built a lot of beautiful ships in Glasgow but, I suppose riveting large sheets of steel together is somewhat different to building a tonearm.
@daveyf - yes, on one level an LP12s ability to be upgraded is a plus, but a lot of the upgrades are aimed at fixing flaws in the original design and engineering.
Its a bit like the restomod phenomenon in cars - yes you can replace and upgrade a lot of the parts but you will still be limited by the original design. And you will spend the price or more of a ground up modern design.
There are other modern designs that offer upgrades - for example, you can upgrade a Clearaudio Innovation to Master Innovation. And in that case you are adding additional new parts and not junking pieces of the existing turntable.
Even where a turntable cannot be upgraded, the economics of trading in the TT for a better model are not necessarily worse than the cost of purchasing parts upgrades. If you do a full set of Linn sanctioned upgrades on, say an 80's LP12, you have almost nothing of the original left except the plinth, platter and top plate.