The wording should state the -static sub-package much require -devel if the -static package is not useful without the -devel sub-package, e.g. the header files are in -devel.

I'm afraid I'm not entirely sure why. I guess BR: foo-static will only very rarely be useful without BR: foo-devel, but then this change would result only in the saving of a line in the spec.

If you want to link against the static library and BR'ed it therefore on purpose, I'd assume that the shared one is not available. Is that a sane assumption to make linking easy to use?

If -static pulls in -devel, one needs to do a bit more work to link against the static one as the shared one should be prefered. Isn't it?

that's not a valid assumption: "I'd assume that the shared one is not available"

We discussed this at today's meeting (https://lists.fedoraproject.org/pipermail/packaging/2015-April/010561.html):

• 522 Should -static packages require -devel (geppetto, 16:41:24)

• ACTION: was voted on last week, and policy changed. (geppetto,
  16:48:06)

Announcement text:

The guidelines for packaging static libraries were amended to indicate that the -static package should require the -devel package:
* https://fedoraproject.org/wiki/Packaging:Guidelines#Packaging_Static_Libraries_2
* https://fedoraproject.org/w/index.php?title=Packaging%3AGuidelines&diff=409506&oldid=405928
* https://fedorahosted.org/fpc/ticket/338