There are statements which are wholly subjective, statements that may be objectively true (but cannot known to be objectively true), and a great many statements which are neither wholly subjective nor objectively true.
"All abilities are magic, and magic is available to all" is part of the implied setting of 4e. This statement cannot be demonstrated to be objectively true, but neither is it wholly subjective.
Anyone who disagrees with that statement may not be wholly wrong (depending upon his criteria for disagreement), but neither is he wholly right. Thus far, within this discussion at least, no criteria for disagreement have been raised that offer more than wishful thinking and/or intentional disregard of the factors that arise from this implied portion of the 4e setting.
RC