Incidentally, it makes more sense they were portable in Japan. The Gold/Silver/Crystal series was renouned for an adapter to play remotely via cellphone. Crystal took it a step further, with special features such as news updates, events, and other patched-in features via cellphone. Really cool stuff, if you ever want to read up on it.
Incidentally, if you ever find Japanese Crystal game with a working save file that's been attached to the network, immediately send it to have the SRAM dumped!!! They have a sort of suicide-clock issue, and with the network down the patched data on the SRAM may never be seen again! (ominous organ music)
Incidentally, even the console variants were designed to have network support, invariably canned when whatever network-providing peripheral they intended to use went up in smoke.
As far as things go though, as a portable game it has more advantages. According to the bean-counters, it isn't expected that users will play a portable game for the length of time they do a console game. So, you take a simple little grind-game with relatively quick story-objectives and place it on a portable. It's expected it is played on/off.
Still, you have to give them credit for backward-compatibility. If you have enough systems handy you can pretty much up-port from gen 1 to next gen. However, much hate and anguish for jerking people around with all the unlocks. At least they don't have you pay out the nose before you find out the system simply won't acknowledge the unlock (not that I'd ever advocate a class-action against EA Games...).