It's more open to interpretation. Fighters and warlords are going to be doing stuff that is very cinematic and fantastic, which could be interpreted as magical. That's reasonable in a D&D world. However, even with that interpretation, the fighter and warlord (and other martial power source PCs) will seem distinctly less magical than members of classes such as the cleric and, of course, the wizard.
That's not a bad idea for a house rule, but just be aware that you necessarily make the warlord a poorer choice as a leader unless the temporary hp he gives seem as good as what a cleric or other leader might give. On the flip side, it's just as easy to imagine that the cleric's "healing" powers aren't actually healing physical damage either.