It's common for projects to state a particular license and then attempt to apply some caveats that remove some of the freedoms offered by that license. I'm wondering if there is any legal basis for this.
Real world example:
pdf.js is licensed under the Apache License 2.0 as shown here: https://github.com/mozilla/pdf.js/blob/master/LICENSE. This appears to be the standard license text with no variations noted either in that file or in the project's README.
In the project's documentation is a polite but easily missed request not to just re-use the code as-is: http://mozilla.github.io/pdf.js/getting_started/#introduction says "However, we do ask if you plan to embed the viewer in your own site, that it not just be an unmodified version. Please re-skin it or build upon it."
My understanding is that the Apache license permits reuse of the code with no modifications at all (subject to other restrictions e.g. trademarks). Thus this request feels like a caveat/reduction/alteration to the main Apache license because it is attempting to remove a freedom expressly offered by the Apache license. Is there any legal validity to this? i.e. if I used the project under the AL2 license, is there any legal reason why I should comply with the request in the second bullet point?
As this is essentially a legal question, I'm looking for examples of where this situation has been examined before (e.g. has been tested in court) or references to the opinion of legal experts in this area. Opinions on whether honoring requests outside the license file proper is a polite thing to do or a standard practice among developers are potentially interesting but out of scope.