How do you determine home comps?

Comps is used to determine home values. Most often it uses data from neighboring homes that were sold within the 6 months. Yet we can only compare numbers. So it's easy to say $price/per sqft, which would be the sales price divided by the living area. There are many popular websites help estimating home values, such as zillow, redfin, eappraisal, cyberhomes etc. And probably each site use different algorithms to determine the final values.

These days home prices are everywhere. Needless to say it's hard to run a computer analyses to give an accurate number. I use Zillow the most, and have found most homes sell much less than zillow price.

Since numbers are 'easier', how come these sites don't factor in lot size? And I would be interested to see if they can one day incorporate other non-number factors in a more systematical way :

1. how much it should decrease if it's on a major traffic road? (this needs to define traffic road first obviously.)
2. how much does it affect the value if it's on T-junction ?
3. how much does it affect the value if the neighbood houses are not update?
4. how much does it increase the value based on school scores?
5. old kitchen/newer kitchen? how much ?
6. old bath/newer bath? how much?
7. floor plan? what type will cause the value drop?
8. how much does brightness and openess add to the value?
9. neighborhood density --- this should not be hard, minimum numbers is just calculate how many homes within certain radius, and I would really like to see this in the comps. It would at least give me an idea before I drive over. I would know if I should expect to see 5 cars parked in front of neighbor's home, or street parking are fully occupied and no space for visitors at all. In fact, south bay can get so crowded that a lot of 2 or 3 bed condos only offer 1 parking space. Even single family houses can have only one car garage, as it was the norm back in the ... 50's??

Online home price estimate can only use numbers based on sales. If there are no similar homes sold recently, it will be far off. It has no idea if the house has any update. It does not know the floor plan. It does not know if the house is having an apartment complex overlooking into the yard, nor does it know if the neighbor has fierceful dogs or drives a noisy motorcycle, or rent out all the rooms so that street parking is always difficult.

As technology advances, can't we have better system to evaluate home values and disclose/compare more information?