Well a typical game now a days has a team of around 100 people. I think Uncharted 2 for example as 120 people. Deadspace has about the same. Uncharted 2 took 2 years. So, if the average person making Uncharted makes $100k a year that would be 120*100k*2+50% for overhead like rent, equipment, health insurance, employment taxes, etc. $36 million If their average salary is only $80k a year then the budget is going to be 20% less or $28 million.
I have no idea what the average salary is on the Uncharted team but you can look at Gamasutra to see average salaries.
http://www.gamasutra.com/php-bin/news_index.php?story=23264It takes that many people that long because there is so much work to do. The majority of those people are artists making the backgrounds and or cutscenes. Every plant, every rock, every temple brick, every tree, every wheel, every tire, every speedometer, every belt, every shirt, every pocket, every shoelace, etc, etc, etc all have to be created.
Diablo 2 was made a while ago so it used a less tech and therefore probably had less details and so the team was not as big. Also the levels are auto generated instead of hand made so that saved some time as well.