Good cartoony movement is certainly hard to get right. A run of the mill 4koma adaptation does not feature good cartoony movement, it features bad shit.
Gurren Lagann, for example, features insanely awesome cartoony movement, and it's no worse than any Ghibli film with literal acting.
K-On! does look very cartoony at times, but more often than not it's timed perfectly and the character designs work wonders with that type of expression.
This is very silly, but the movement itself is nuanced and has a very soft feel to it, which in turn makes cuts like these warm and fuzzy, which is exactly the objective of the show. Have a look at the hand on the second gif and how she plays with the orange; there are a lot of little details like this throughout every episode. Mind you those are not the best examples, I just googled some random parts.
And a lot of the time you do have some solid "traditional" acting too
This may not be Inoue or Iso, but the range of expressions she makes, and the pompous way in which she does it tie in perfectly into the context of the scene (for anyone wondering, it's in S1E01). This is good character acting, of a kind that is rarely seen on TV.
As a corollary, character acting is not the be-all-end-all test of slice of life animation. Everything in K-On!, whether it is cartoony or more realistic, is very polished, and the sketchy movement and lineart are done on purpose, because that way the animation style goes hand in hand with the tone of the show. It's a distinct approach to animation, and for me it felt like the first time people over at Kyoani sat down and thought about what their movements and way of expression were conveying in and of themselves. The amount of effort that went into the show is ludicrous, and dismissing it as "cheap cartoony stuff" is kind of insulting.
Hyouka's approach is different, and really really good too; but even there the Horiguchi influence is really noticeable, and the show's animation wouldn't be nearly as remarkable if it followed in the vein of Haruhi 2006/KEY's half-assed style.