Nickster's First Law of Prototyping: There is an inverse relationship between the seniority of the stakeholder and their ability to visualise/conceptualise interactions from a low fidelity prototype...i.e. the more senior they are, the more fidelity is required.
Whether they cannot or will not is kind of moot, but accept it as a fact of life. They become distracted or diverted by detail (e.g. example copy) and the tunnel vision that ensues does not encompass what you are trying to convey (in general but not always).
Read Marty Kagan's "An Open Letter To The Design Community" as it covers this ground very well. Mandatory reading for all imho.
Personally I now use wireframes for my own design iterations and Axure for anything that needs presenting to stakeholders.