What the first writeup fails to deal with is the fact that the razor companies (Gillette et al) sell the handles at a loss, or they give them away with a purchase of a certain number of razor blades to fit the handle. This is a cunning ploy to get you to use their brand of razor, and all these gimmicks like 4 laser-sharpened, diamond-tipped, samurai forged mini-swords help re-inforce in your mind how wonderful a new razor is.
This all comes from when King Camp Gillette invented the safety razor, the first safety razors used a common blade which is a pattern stamped from sheet steel and sharpened on the edges. Before long, other companies started copying the design and using it in their own razors. So Gillette started making changes, and therefore we get to the situation today where every razor needs a different blade. And a pack of eight blades for a Mach 3 costs ~£8.
(A bit like the situation with printers, manufacturers selling the machines as cheaply as possible, then making a killing on the ink.)