I just pissed myself laughin at this thread.
Clubber i can see your point that yes people do refere to aluminium frames as "Alloy" but thats because they don't understand the term.
The numbers in 6061 and 7075 (Aluminium) and 4130, DN6 853 etc (steel) indicate what the tubes are made of. This is because pure Steel, Aluminium and Titanium are generally unsuitable for frame building so they have to be mixed with another metal to be more effective, Hense Alloy.
I'm sure someone will be able to do a better job of saying all that.