Tht's a good indicator that the stays on the lower of the two bicycles are almost certainly a lesser grade steel, probably hi-tensile. Marketing people are very adroit at using lack of information (i.e. if they don't state the stay material, the marketplace will think they're the same as the main tubes). They can't be sued if it isn't stated and the public makes the wrong assumption.

At one time, you could fairly safely assume the stay and fork material by whether the dropouts were stamped or forged, but by the early 1980s forged dropouts started to trickle down to the entry level models with hi-tensile stays and forks and you had learn how to correctly interpret specificatiopns and tubing labels.