I think its not because " they are not as valued " it as more to do with them not being a endangered specie therefore there is no need for a proof of origin .
my 2 cents
Blacks arent endangered and aren't on CITES list so they're not chipped. Greens are part of asians which are on the list, hence why they are chipped despite being cheaper.
Asian arowanas are on the CITES Appendix I list (most endangered) and the chip is to prove they are bred from F2 (I think?) stock. Have a read: http://en.wikipedia.org/wiki/CITES#Appendix_I
Pimas are on Appendix II, which means they are threatened but not critically endangered.