13 / 13 splits have been around for about a decade and have nothing to do with how Bandai manages its mainstream properties. Anything you see produced as a 13 / 13 order is basically the result of someone not being willing to fully invest in a project until they see how the merchandise sells in Akihabara, because no other source of profit is likely.
Bandai's big franchises, including Gundam and Rider, are expected to get traction outside of Akihabara in order to be successful. Anything produced 13 / 13 is just not in the same league and not worth talking about in the same breath.
Splitting a 50+ episode pitch like 00's in half isn't going to have anything to do with Bandai somehow being too poor to pay for full production cycles (and for 00 they paid for it all up-front anyway). It's sure makes no sense as a reason why Bandai would want to split up the production order of a super-guaranteed cash cow like Decade, where the toys are all going to appeal to multi-generational audiences out of the gate.
Slayers Revolution/Evolution-R is anomalous: it's being produced to ape the style of Slayers NEXT and Slayers TRY back in the 90's, since the whole point of that project is nostalgia. They were planned and funded at basically the same time, and the division into two "seasons" is pure artifice. NA distribution rights to Evolution-R were sold with Revolution's, in fact. It's really just one series for all functional purposes.
Anyway, uh... a 60-episode order for Decade is ludicrous, even if the "two seasons" rumor pans out. If they didn't give even Den-O that many episodes at the height of its popularity, why would the same network suddenly be willing to give up its Spring 2010 premiere slot ahead of time in exchange for a huge order of a show with a weird, frankly untested premise? Something's just up with Decade that hasn't been revealed yet, I think, and may not be revealed for awhile.