WOW! What an amazing point. which i have never heard made before.. I'll bet you are absolutely right. There has to be a reason these machines can't be cleaned properly once they have been so clogged with the limescale

There is one proviso however, which is that not all machines have the same material composition to the water chamber. Surely it would be easy to obviate this problem by making the chamber of (eg) stainless steel.

One of the currently-acknowledged 'best' machines, the Gaggia Classic uses a curious boiler with an extremely limited life made from aluminium. I have a similar machine called a Baby which I bought second hand which, when enough citric acid had been passed through it to clean off all the limescale, started passing out black dust which seemed to have nothing to do with either limescale or coffee residues. When I dissembled it, I found extensive pitting which was so bad that in places it is 2-3mm deep! No one on the Gaggia forum seemed to have much idea about it save to blame the user for build-up. I can't see it can have been anything other than blackened or oxidised ally?

On your other point, there aren't any machines which either make the boiler easy to take out or treat it as a consumable which is going to need replacement every half-decade or so when used in places with a hard water supply?