S, M, L against numbered sizing

When I see S M L kind of sizing I shake my head a little.  Especially if the outfit in question is priced at a fairly high price like a $600-700 leather jacket.

I take it it can have XS, S, M, L, XL and for numbered sizing 36, 38, 40, 42 and 44.  So are they same?  I really don't know.  I tend to think when one uses SML sizing, it's just a bit unrefined and for lower priced goods.

Many if not most manufacturers still not disclosing what those letters or numbers mean exactly even for those selling online.  I think that's crazy.  Does 42 mean the jacket is 42 inches pit to pit or it means it's supposed to fit body with a chest size 42 inches?  Even for those sites that provide a size chart it's not clear to me what 42 means.  I wonder how can online retailers get away with actual measurements.  Some sites say true to size, what does it even mean?  Just give out the true garment measurements already.

I feel like eBay sellers do a much better job in general.