That is true, i just don't think that even if it happens to be a word that looks cool with a 'z' that it would be all that easy to find an end user who agrees it looks cool and would be keen to use it as a name and pay good money for it in the .co.uk space.
I'm sure similar domains will have sold in the past, but i reckon a lot will have been allowed to drop.
I would love to be proven wrong though and for you to make a nice flip. Also I'm not saying it's rubbish, because it's not, it's just not a side of branding that floats my boat personally or one that i would try to push.