I don't see how his OBP would decline if he hit 15-20 homers. If his approach is patient line-drive hitting, attempting to hit more home runs would change that approach. It's not some for-certain thing, but it seems reasonable. Hasn't Ichiro also said the same thing...that he could hit for more homers but he'd overall be a less productive hitter. I believe he's put on quite some shows in BP. Guys with superb bat control and pitch recognition (not talking about race at all) like Ichiro and Fukudome probably could hit for more homers at will by lofting the ball more and swinging at pitches they could elevate. But fly balls are turned into outs much much more than liners and grounders and by having to be either more or less selective (based on what the pitcher is throwing them), there would definitely be an impact on OBP, as well as other stats. Looked for the quote, couldn't find it, but I recall a Ghost of Mariner Past (Buhner maybe?) saying that Edgar Martinez and Ichiro would go back and forth in BP and everyone else would watch in awe. But the quote also alluded to what you were saying about approach, i.e. less productive, etc.