It seems like Canon currently offers three tiers of prime lenses:
$$$: 50/1.2, 85/1.2, 135/1.8
$$: 24/1.8, 35/1.8, 85/2
$: 16/2.8, 50/1.8
I first thought, why do we need a lens between f/1.8 and f/1.2 ?
We can just buy one or the other.
But there's clearly a distinct $$ line with IS and macro.
Here are some claims without proof -- so any of this could be wrong:
* Canon's total profit for $ lenses >> Canon's total profit for $$ lenses.
* Canon's total profit for $$ lenses >> Canon's total profit for $$$ lenses.
* Three tiers cover a significantly wider market than two tiers.
* Four tiers cover about the same size market as three tiers.
Now, in what order should Canon roll out the lenses ?
If Canon only made $$$ lenses, they wouldn't make money.
If Canon only made $ lenses, the pros wouldn't be happy, and they wouldn't tell the newbies how awesome Canon is.
If Canon only made 50/1.8, 50/1.4, and 50/1.2, then nobody would be happy.
So it seems like a non-uniform roll-out is a pretty good idea !