Keep in mind that there is another common reason why former facebook friends do not come up in searches: they may have deleted their facebook account. I find that this happens much more than people realize. In fact, I've done it myself! Here is what concerns me about my experience on facebook: I left it for about a year (which obv resulted in me not showing up as "friends" on all of my former friends' accounts and some of them could have gotten wrong impression from this), but then I decided to reopen my facebook account (so I had zero friends starting out again). I sent friend requests to maybe 50 of my former 500 "friends" or so (as I did not really feel like going back and adding everyone. Most of them were just acquaintances as I had been in a situation for a couple of years in school in which many people knew who I was that I didn't even know personally, and those that I did know I hadn't seen in 7 years anyway). But here's the drawback of what I did--there were 450 or so people that I did not "refriend", and I'm willing to bet that a number of them noticed that I was back on facebook and did not add them (in fact, many of them probably never knew that I was gone for that year anyway, so they probably got the impression that I actually took the time to delete them as a facebook friend! It's possible that some of them may have taken this personally, although I hope this is not the case, b/c it was nothing personal against any of them.)
So the long and short of it is, I wouldn't jump to conclusions if I were you because you don't know what happened. And even if one of your facebook "friends" deleted you, that's pretty lame that they would actually take the time to do this. And you probably don't really want people like that in your life anyway.