A primary concern of Pokemon Diamond/Pearl (or, at least, that of this blogger) is the incredibly rampant cheating. In the past, use of an Action Replay wasn't a horrible offense ... your team would be uber, and a couple of your personal friends might be a bit ticked, but that was all.
These days, in the era of Wi-Fi, ridiculously impossible trades litter the GTS. What, you don't have a Level 100 shiny Palkia? Well, hmph, you can't have my Level 7 Munchlax, then. For honest players, or those that don't have access to hacking tools, such Pokemon would take days to train up and impossible luck/determination for one with shiny status. That's why we're happy that Nintendo is cracking down on some Action Replay users, specifically ones using the "All 493 Pokemon," "All Shiny," and "National-Dex" cheats. They will henceforth be banned from online barter.
Feel free to start a flamewar regarding the justification of cheating, by the way. We're pyros.