Well, two things. One, CMR shares some traits with other 'old' fonts (sometimes actually old, other times aiming for a dusty or scholarly air): lots of variatio

Well, two things. One, CMR shares some traits with other 'old' fonts (sometimes actually old, other times aiming for a dusty or scholarly air): lots of variation in stroke width, relatively prominent serifs, a 'true italic' where some italic letterforms look much different from their roman counterparts. (Knuth was making these for a textbook, so maybe he went for a look similar to textbooks of the time, at some intuitive level at least.) If you look on Google Fonts, Playfair Display and Old Standard TT do some of those same things in (I think) also aiming for an old-timey air. So, I think some of the "air of respectability" comes in part from traits shared with some other fonts, not just from appearing on math papers. Two, the "feel" and aesthetic aspects of a font mostly do come from memory and associations. nytimes.com doesn't use a serif because it's more readable on the Web or something; they do it because serifs and newspapers go together in most folks' minds. Even the most thought-out arguments about fonts have associations as their bedrock: when Robert Bringhurst laments that a font shows no real axis with its variations in stroke width and therefore fails to evoke calligraphy, the axis he's missing is still important "merely" because of its association with calligraphy. Other than purely technical arguments about readability (which you could dispose of with an A/B test), most opinions about fonts are, one way or another, rooted in associations. So if folks do appreciate CM partly because of their experience with it I don't see anything illegitimate about that (unless maybe it were utterly unreadable, rather than just quirky). You don't have to use or like the CM fonts, but I don't see how anyone's clearly indisputably wrong for liking them either, any more than with any other font.