Well, it makes sense that he retires, there were no signs that he could really come back... Sad, anyway.
If you check by the 2008 tables, his 2:06:17 is the best American running performance ever (only Khannouchi obviously faster), taking into consideration all distances from 800m to the marathon!
His best race in terms of place being the 2009 Boston marathon with the third place - a top three finish is not going to be happen often for Americans in any long distance race, let alone a WMM race.
Good bye Ryan, you were a great motivation.