I think this app note is most notable for what it doesn't contain: eight pages of circuits for clocks and oscillators (including a sinusoidal oscillator; see Figure 9), yet no mention of Wien bridges or his treasured HP200. Curious. Most of the circuits here include quartz crystals, but not all of them: Figures 11 and 13 are synchronized to 60-hertz line frequency, and Figure 15 is a "stable RC oscillator." A discussion of a Wien-bridge oscillator would have fit nicely into the theme.
I agree with his characterization of the circuits in Figure 1 as "temperamental". Despite these circuits' common use, there's a reason why Colpitts, Hartley, and Pierce are still household names. (Well, OK, not quite "household names", but you, dear reader, my educated friend, you should know them.) The box section on page AN12-8 is a one page discussion of quartz crystals, which is good reading for the uninitiated, but not really enough information to dispel the mystery.
Two approaches for temperature compensation are shown. Figure 5 shows an ovenized Pierce oscillator, but the best circuit is Figure 6, a Colpitts oscillator with a temperature-compensation loop using a thermistor and a varactor (very similar to Figure 21 back in App Note 3). The results shown for the temperature-compensation loop in Figure 7 are impressively flat.
Best quote (from page AN12-1): "In consideration of these difficulties, gate oscillators are generally not the best possible choice in a production design." Listen to the man, he knows of what he speaks.