Perhaps. But note that Apple used to specifically tell you not to use case-sensitive HFS+ for your boot volume in the 10.3 days. See the first paragraph:
While this is true, "Apple" also goes out of its way to fix build problems (internally) that result from case sensitivity gone awry. I don't think MacPorts should hide behind this one - it's not a very future-proof strategy. I'll say no more. :-)