I agree and disagree with some of the points here.
*IF* The shell wants/needs you as a certain job class, i.e. they need you in sky as RDM and at say an O-hat Run as a NIN... common sence would be that you go with the job class that is needed most so that you are not simply being a waste of space unless you just hate the job you're being asked to use. Two reasons most end-game players focus on a second job: They become tired of their main job (find another job that they find more fun for them to play) or want to be more versitile for any sittutation that they might be in.
It is not as uncommon as you might think for a person to always go to sky as one job and use the time to obtain gear for another job. That holds true not only in sky, but anywhere. If BoL told you to declare a main job (which I do believe that is how they do things) and you didn't, shame on you. Now if you say you want obtain NIN gear instead of RDM gear and they always need you as RDM and refuse to allow you gear on your NIN because they need you to play RDM, shame on them. Make sense? People with multiple jobs at 75 seem to always throw off the rules because most rules were created way back when most people only had one job at 75.
I've always held slight respect to the idea that gear should be distributed to members based on the idea of bettering the linkshell as a whole... but to me personally, I find that you're far better off bettering the individual for the good of the whole. Strangely, it is much the same... but quite different. It's sorta the reversing of "What can you do to better your linkshell?" to "What can our linkshell do to better 'our members?" In the end it doesn't matter, as you'll leave and BoL will have another new bloke to take your place.
To BoL: Last week's flame was much better. Rate Down ^^p
To the OP: Just some advice. If you have numerous high-end jobs leveled (especially rdm and ninja) than I am sure you won't have trouble getting into another end-game shell. Just realize that most of those shells are not just going to "give" you the item you want because you show up everytime that byakko is popped. Show dedication, put in your time, and most importantly read their rules and figure out how they do things before you invest a lot've time into stipulations that you might not personally agree with.
To Shaidalyn: The reason that a BLM who might not receive anything in sky would continue to be in sky is that they might actually enjoy it or simply enjoy the people that they do sky with. It's not uncommon. If neither is true, than I think they're simply werid. ;o If you remove and/or ignore the drama of end-game it is actually a lot've fun.