It's not the matter of $20.00, if you have a look at the big picture as follows...
These are estimates only.
350000 Hilux V6's have been sold from 2005 to 2009.
Out of those 350000 Hilux's sold maybe only 1700 will ever have LPG fitted by the owner.
Do they put the price of 350000 Hilux's up by $20.00 to cater for the 1700 people who want LPG or do the cater for the 348300 people who didn't.
It's to do with economics.
But we don't know the reason why they run soft valves....in their testing they might of found out by using softer valves they can extend the valve replacement time from 160000 kilometers to 390000 kilometers.
It might be they can save 30 grams in weight a valve by going to softer ones (24 valves at 30 grams = .720Kg of weight savings).
The softer valves may open quicker and the don't have to run as stronger valve springs helping fuel economy.
Toyota would do there market research and know spot on what people want out of a vehicle.
I run my business the same...I provide and sell what most people want, this is how I make money.
If I didn't want to make money I would provide and sell what most people don't want at a price they would want to pay.
Or if I wanted to make money I would increase the price of my services and products to cater for the minority of people and loose the majority of people....At the end of the day the minority of people wouldn't want to pay more for me to cater for there requirements so I would loose money.....I would be better putting my resources into suppling the majority.
It's not rocket science.
Learn to live with it.