Surely weaning is like everything else with children, there are no hard and fast rules. I suspect that most babies are probably about ready for solids around 6 months but for some it's earlier and some it's later.
I also think the allergy argument is a bit thin in hard evidence. My DD1 is allergic to LOADS of things, she was showing allergic symptoms BEFORE weaning (proteins passing into breastmilk). I belong to an allergy support group and all the multiallergic children I know showed symptoms before weaning.
Also can't bear this crap about iron levels in breastmilk not being enough after 6 months. My DD2 is 12 months and still hardly eats any solids at all. She refuses solids and is thriving on breastmilk, I am assuming that she knows fine well what she is doing.
If she needed solids she would eat them. She had a blood test recently for allergies and had iron levels checked too, they were of course fine.
My nephew on the other hand was weaned at, shock, horror, 4.5 months!!
He was hungry, he wanted solids, he was given them, he was much happier. My sister was reluctant to do it but is sure she did the right thing FOR HER BABY.
Arbitrary rules like 6 months or whatever may be guidelines but babies are individuals and some are ready sooner, others later. As a previous poster has said, if you follow your baby's cues and have a bit of common sense then you can probably work out for yourself what is best for your baby surely?
As we say with breastfeeding 'watch the baby not the clock' for weaning I would say 'watch the baby not the calandar or some parenting manual that some so called expert who may or may not know their stuff is trying to sell'.