You are right, the fan speed should be related to current (or just previous) processor and graphics load.
There are a few things you can easily check to see if there is something wrong.
How high is the ambient temperature?
Cooling in a tropic climate will be harder. This shouldn't be your issue, just mentioning this for completeness sake.
Make sure the airflow in and out of the VAIO isn't obstructed!
Are you using the VAIO on a flat, hard surface (desk, table, counter, lap-table) or on a soft, plieable surface?
Your answer should be the former. Fluffy isn't good in this case, since while it might beautifully shape itself to the VAIO's bottom, it'll prevent air from brezzing by and taking heat with it - or being sucked into the vents.
Make sure the heatsink isn't clogged!
Any pet in the picture? A smoker? Is it being used in a kitchen? Dusty place? Combination of the above? If a melange of dust and hairs, with or without bonus nicotine or grease clogs the gaps between the cooling fins of the heat sink, it's effectiveness drops rapidly leading to a very hard time for the cooling system and the fan. You can check this both by your use situation. You might or might not be able to see stuff clogging the heat sink from the exhaust - there might be a felt of stuff on the fan side. If your conscience isn't clear, you can use compressed air to dislodge the bits from the far side of the heat sink. Be careful applying it, don't overdo it, don't use a vaccum cleaner. Obviously, don't bother with this if the risk factors don't apply or not enough time has elapsed.
Is there any BIOS update available?
The temperature control is done by the BIOS, if there is a BIOS upgrade, it might have something to do with the cooling. If someone else has reported a problem which was resolved by an update, you want to have that update in so you can forget about an issue that was already solved. So if there is a BIOS upgrade, install it.
If you've considered the points above and there is still no reasonable explanation for a high fan speed, check with the VAIO support line and see what they say.
