Most organizations would benefit from standardized development guidelines. Some product managers try to put these in requirements but they really belong in a development (and design) standards document. Development guidelines imply performance and constraint requirements, those non-functional requirements that often make the difference between a good-enough product and a great product.
In a related topic, have you started using Personas? A good persona document also includes performance and constraint requirements, such as the skills of the persona and their computing environment. If you know Robin has Windows 7 and Sarah has a Mac, you know what operating systems you need to support. Since Curt is working in construction, you'll know he may not have access to power or WiFi. Because Nana is unlikely to travel outside her home country, her phone doesn't need an international calling plan.
Don't confuse requirements with implementation. (See On Reqs and Specs for more on this topic).
Apple Human Interface Guidelines for iPad
iPadHIG.pdf (5777 KB)
View this on posterous
You can download the Windows User Experience Interaction Guidelines from http://msdn.microsoft.com/en-us/library/aa511258.aspx
(side note: the properties of the Windows User Experience Interaction Guidelines PDF are "fake TOC." I dunno; just make me laugh.)