Let me explain..OEMs give a price to MOs on the update services. These OEMs have consistently underestimated the number of upgrades and work required to get updates to the MOs.That under estimate impacts the resources at the OEM brought to bear on the problem.
If you're right, then most OEMs are really missing the boat by not engaging with the Android ROM development community more seriously. Cyanogenmod (and other community projects) have already done (for Gingerbread) and are already doing (for ICS) most of the non-customization work (including many of the tedious parts) required to produce OS updates for almost all devices with an unlockable or hackable bootloader, including many of the phones that currently fall through the cracks.
If OEMs focused on resolving key roadblocks (like binary graphics drivers and the 911 issue that made Cyanogenmod drop a few phones) and getting updated phones through carrier certifications, they'd spend less money and get more phones upgraded and would have a more customer-friendly, transparent process to boot.
The development part of upgrades is not a problem, neither resources or time-wise. The real problem are certifications. Alternative firmware developers like Cyanogen or MIUI do not have bother with this, they are not selling products based on their software, but phone vendors have to go through them. This is the big sink of money and time.
Recently, there were articles by Motorola and Sony Ericcson, that shed a little bit of light on this topic.
Let me explain..OEMs give a price to MOs on the update services. These OEMs have consistently underestimated the number of upgrades and work required to get updates to the MOs.That under estimate impacts the resources at the OEM brought to bear on the problem.