No, they could have changed it if they wanted to. Service mode is a backdorr Sony put into the PSP, they could have removed it if they wanted to.
As for the 3000, Pandora doesn't work because Sony blocked the serial the battery uses and blocked the exploit it was using to boot in the CPU.
Sony also locked the Pre-IPL down and that's the main reason why the 3k hasn't been hacked. If\when the Pre-IPL is accessed, the 3k will fall.
Lastly, just because the Go doesn't have a removable battery, doesn't mean it can't be hacked.