in fact nothing strange there. Series 40 phones are based on NOS and are more like traditional mobile phones. They are propably cheaper to make since you don't need to build all the stuff that symbian requires as well you don't need to pay for the OS lisence, since the OS is owned by manufacturer. That's basically what all manufacturers are doing.
You can still make applications for it with Java MIDP, more restricted thou, but serves a great number of customers.