Richard, the reason why you don't remember it is that it was a lie. The true detailed reason is that it is awful lot of extra work for the tailor, who has to make clean every single seam on the inside (tape or turn and handsew the edges), which would otherwise be hidden under the lining.
Sartorialist, make no mistake, all-season suits are like all-season tyres: you don't get performance out of them in summer and traction will be poor on snow in winter. Therefore, my advice is to have summer suits made for summer, winter suits made for winter and wear what you please in-between the extreme seasons. That said, summer suits benefit most from the use of porous cloth tailored in unlined jackets and trousers. Porous weaves (that favour ventilation) are made with thicker yarns and the resulting cloth is heavier, too - which is an added benefit as it will tailor, look and behave better. Look for frescoes (fresco is not a type of suit, but rather a type of cloth) - the light gray example above is an excellent London Lounge Cloth Club special issue called "Brisa" -, linen and, yes, mohair.
Detailed discussions on the choice of cloth, construction etc. for summer suits abound on the LL - if you can't find them using the in-built search function (which only returns posts dated after the LL redesign), you may use good old Google typing "site:
www.thelondonlounge.net" before the keywords to search for.
