If you look for the price of the Canon 24-105L/F4 on Canon's website then:
Thanks for showing me the price from canon, but I think you know the real marketprices. And yes, new lenses have to compete with older existing ones.
Un, no. Most people will quite taking photographs due to the elements well before their equipment is in danger. Do you think most of the 24-105's that Canon have sold get used in the rain? Most people will want to be inside and out of the rain first.
Most of the 24-105 were just the first lenses on a fullframebody and yes they would've been sold without sealing, too. But I think if you're working serious with photography there are a lot of situations when you need the weathersealings. At least I do. On a Lense with a pricetag at some hundred dollars there should be some pennies left for some rubberbands.