Bug report

The "sample plots" in the tutorial sections should all use the same method of generating a new plotting axis, unless the tutorial is about different methods for achieving this.

On this page:
https://matplotlib.org/3.2.1/tutorials/introductory/sample_plots.html
Most of the MPL examples now use plt.subplots(), EXCEPT for the following:

• "Surface3d" (gca),
• "Multiple Subplots" (subplot),
• "streamplot" (fig.add_subplots),
• "Polar Plots" (subplot),
• XKCD (fig.add_axes).

Expected outcome

If it makes sense, I think all of these should be converted to use a single style of figure/axis creation. Possibly also applicable to other tutorial pages and examples in the documentation pages.

@tacaswell suggested that plt.subplots(...) is the preferred way to do this, so the above could be unified in using that method.

(Here is the SE question prompting this bug report)