I don't see why that's the case for Lenovo though (which I'm most familiar with - Thinkpads), since you have to order online. They could do batches of different configurations, it might add a small delay for particular configurations, but that would be ok. What they do now, mostly limiting larger RAM/storage configs to top end CPUs, seems like an upsell (though at least their storage is usually replaceable, and aftermarket offers better price/choice, though the spare small capacity device is a waste).
In Apple's case, it simply seems like an upsell. They must have enough volume to sell lower spec, large storage capacity Macbook Airs at stores, or online.
Most people buy low end machines from Apple. They just keep volume handy. Although recently when I went to Apple store they had no stock at all here in the UK of anything. Literally emptied out.
Yes, but how much does it cost Apple to put a larger volume in, compared to what they charge the consumer for that one feature? I have very often seen Apple users hampered by this, including losing data due to having to juggle external storage. Upsell.
In Apple's case, it simply seems like an upsell. They must have enough volume to sell lower spec, large storage capacity Macbook Airs at stores, or online.