As long as LevelDB supports all of the platforms and performs better, then all is good.

My reasoning behind SQLite (only for wallets, not the blockchain) is that is supports native SQL syntax, has many DB tools, is portable between platforms, supports almost every programming language and supports compression and encryption. Performance when under 1Gb in size seems to be excellent and it is widely deployed (like Adobe, Skype, Dropbox and many others).

I updated the OS list.