At .250" thick, the BK-2 is an incredibly strong knife; however, it's heavy. At .188" thick, the BK-10 is noticeably lighter, yet it's still a very strong knife. No, it's not as "bomb-proof" as the BK-2; however, it's still very strong.
In my opinion it comes down to how strong you feel you need your knife to be. Does it need to be "incredibly strong", or is "very strong" good enough. If "very strong" is acceptable, then I'd opt for the BK-10, since it's lighter. And remember, the BK-10 is the same thickness as the BK-9, and guys baton the heck out of that thing without issue.