I beleive the reason codes are actually part of the FICO system from Fair Issac. i.e. Reason Code 8 is "Too many recent inquiries last 12 months". Underwritting systems can choose to add weight to reason codes. For instance if the bank that issues the a card is concerned about churn they may opt to ding you an extra 20 points for a code 8.

The long and short of it is using FICO greatly reduces the underwritting process for the bank. FICO take the 200+ datapoints from the actual credit report and converts it into a simple score with about 40 or so plain english reasons why that score is the way it is.

For reference, here's all the data provided by Experian that makes up your credit report.

http://www.fairisaac.com/NR/rdonlyre...buteValues.pdf