Steel is easy to weld. Speaking as someone who's only done it once, and passed the test at uni (not a very high level, I may add) without ANY practice, I think its safe to say steel is piss to weld. Brazing may be different though, I'm not sure (how Leesons are held together). Clive probably used brazing since its easy to blow through thin (less than 0.75mm) steel tubes when welding - brazing is at a much lower temperature. Having said that, to construct with Reynolds tubes you need to be certified - so I have no doubt at all Clives very skilled. (I'm probably wrong about some of those details... someone feel free to correct, but that's what I recall :sleeping:)
Anyway... aluminium welding is MUCH more difficult. Those welds are sweet as a nut. Give me a mass produced aluminium frame any day, they'll always out last, out-value, and out-weigh (be lighter) a steel frame.
Topic in hand - how very irritating having so many 'different' frames, which are all essentially the same.