The thing is Bec that there have been numerous studies now and no benefits have ever been found to be associated with the early introduction of solids - except for the baby food companies.
The problems with introducing solids too early aren't just that it's associated with increased risk of a range of allergies. It can also cause nutritional deficiencies in cases where solids replace too many milk feeds and encourage over-eating leading to increased risk of obesity.
It's not just WHO that recomends delaying the introduction of solids. All the state governments in Australia, the American College of Allergy, Asthma and Immunology and the American College of Pediatrics (to name just a few) also recomend delaying the introduction of solids until 6 months.