I think the thing to consider is that this advice and research refers to allergies only. Intolerance to a particular food is a different thing entirely, and has more to do with intestinal development and digestion. As an example, some babies (and adults too) may not process highly acidic foods such as tomatoes and oranges easily, which may cause stomach pain, so these may need to be avoided or given in minimal quantities until they can be processed without causing discomfort. So whilst the advice is certainly useful, I don't think it should be taken as a nutritional panacea, there are other reasons why some babies may benefit from a later introduction of certain foods. Given that this is strictly a study on allergies, the single-minded focus is not surprising.

It concerns me a little that the researchers did not make specific mention that foods like honey still need to be avoided due to toxicity concerns, whilst they do say to monitor reactions, toxicity from honey is generally cumulative.