Bush vs. Kerry

for "布什" "凯瑞", I get
简体中文网页中，约有 11,800 项符合"布什" " 凯瑞"的查询结果

for "布希" "柯瑞", I get
關於"布希" "柯瑞"大約有1,410 頁繁體中文搜尋結果

I suppose the mainland preference for "布什" is because the final "sh" sounds less like the equivalent of pinyin "x" and more like "sh" to mainland ears (unless they're being guided by spelling). Whereas in Taiwanese Mandarin, they don't retroflex as much, so the final sounds more like what is rendered as "x", hence "布希".

While I had trouble with 凯 at first, I've got to admit it does sound like the English. Why do the Taiwanese use 柯? Maybe it's a Taiwanese Mandarin thing (they couldn't be influenced by spelling, could they?) As for 瑞, which both use, that makes no sense to me at all. I would have chosen some variety of "li". Maybe there are too many Kellies, so they wanted to distinguish him from them.