For example, counting has nothing to do with the numerals or the decimal system. Start from the concept, not method for its presentation. Manipulatives are not the end goal of education. Use them to present concepts, if necessary. Grasp the difference between the abstract and the class.
Class is a concrete description of the abstract.
A concept that can't be represented as an object class may be too broad an abstraction to teach. Be consistent and honest across selection of presentation vehicles. If using measurements is a proper way to introduce geometric concepts, then using the Roman numerals is a good way to introduce counting. Emphasize relationship between concepts.