Having worked with the system described in the past, it's quite flexible: data can be easily pulled out into more specialized systems for aggregation or trend analysis, while the raw logs remain quickly accessible over long enough periods of time to allow for digging into everything from support cases involving a single person to monitoring distributed attacks. Access can be controlled and monitored with reasonable granularity, and training new folks to use it is as easy as teaching some basic Select queries.
Not gonna suggest it's the most efficient system (if nothing else, SQLServer wastes a TON of disk space), but it minimizes complexity while deftly avoiding the choice between throwing away information when it's still needed and keeping everything in flat files which are too unwieldy to be used.