It always takes longer through a reseller. I think Apple's priority #1 is orders through their online store thus orders made by resellers may take longer to be built. That 2-4 weeks is just an estimation, I've heard people having to wait for months to get theirs. Also, resellers tend to know nothing about the schedule so it comes when it comes, or if it comes.
Always buy BTOs straight from Apple unless you want to keep waiting