Mage Black, it could be that Balmung just has fewer spambots. Maybe people on Balmung don't buy gil. Maybe you're just in instances often enough that you don't get targeted. Maybe your character name is somehow resistant to whatever character-polling algorithms the spambots use to find their targets. I do know that my experience is not the same as yours. When I was blisting every spambot, I was having to clear my blist every 1-2 weeks. I've since stopped blisting most spambots (I only bother if I'm in the middle of a /tell conversation as it removes the bot from the /r list so my /r's go to the right person, or if the spambot tries to friend me). My blist is still filling up quite fast.
If you've never had to clear a full blacklist, it's a huge pain. You have to click each individual name and then click confirm. Deleted characters are not removed from the list automatically either, and each (Deleted) name has to be individually removed (each with its own confirmation window). The confirmation windows are irregular in size due to large names causing text to wrap, so the "ok" button moves, preventing you from click-spamming to delete a series of bots. So, it's click, move, click. Click, move, click. 400 clicks total, with movement between each. (On a side-note, if the EMR company I work for had an interface like that, doctors would be up in arms about it and we'd lose customers. "Click reduction" is seen as a serious performance concern here, so I cringe when I see interfaces that aren't designed to minimize clicks.)
On a side-note, I really do hate the new spam-bots that do not send tells, but instead spam friend requests (I think they're on trial accounts?). If you accept the friend request (I did once out of curiosity), they moogle-mail letters full of spam. My problem with them is that when I get a friend request from what's clearly a spambot, I hit my "flist deny <r>/blist add <r>" macro. In this case, instead of denying the friend request and blisting the spammer, I blist the last person who spoke to me via /tells (provided they're not on my friend list already).