This is just my 2 Cents;
When Konami made the much acclaimed edit mode in PES4 on the PS2, pretty much the whole PES market loved it, you could do some pretty nice things such as changing and editing emblems/sponsers. Now when they released WE9/PES5 they were working on pretty much the same console in the same generation (Xbox and PS2), it was a straight forward port.
Now, the same was done with WE10/PES6 on the PS2 - the developers had to pretty much carry forward the edit mode into the next version. Think of PES6 to PES5 on the PS2 as a minor update.
Now, turn your head to the x360 - Konami didn't promise everyone a next gen title when PES6 was confirmed for the PS2. Anyway, I digress - Konami had to basically create a new game, with new developing tools, on a new generation console. It is this reason why they couldn't just port the edit mode from the PS2 to the x360. Theoretically it is possible, in practice however Konami couldn't do it, as they would have to build a brand new edit mode from the ground up. This would include painstaking work such as implementing custom designs to shirts and boots and faces - they simply couldn't do it to a sufficient level for retail. Which is understandable seeing as this is their first next gen title.
All this talk about "copyright" seems a bit condradictory, as PS2 & the PC harbours a full-on edit mode, where as the xbox 360 doesn't.
As for the Xbox Live Marketplace speculation, I doubt Konami will release an edit mode through it, if any. And if Konami were to release purchasable PES marketplace goods it would probably come in the form of themes and picture packs and what not.
Who's point seems more valid?