Why is this an "obstacle" for iTunes? It's unfortunate that they "had to" create multiple storefronts, but they didn't do it because they wanted to fragment the iTunes store, and being able to consolidate the storefronts will be a benefit for Apple.

The old licensing scheme (the current one) is the obstacle - it was really hard (and slow) for Apple to set up all those separate stores, with different content in each one.

A pan-European licensing deal would remove that obstacle.

This will pave the way for multi-national record companies to plow through Europe and destroy the cultural diversity that exists right now.

They whiners that don't like the pricing should move elsewhere for a while and come to see how good they actually had it before.

It may destroy the network of licensing organisations and companies that hinder distribution of material. Currently some material is not available in all markets because the local licensing hasn't been agreed.

It may not be, say, Universal Music withholding the license, it may be whoever holds the license for Universal Music properties in that country.

People wishing to perform certain famous musicals in France must negotiate with the rights holders in New York, as they are the "local" agents for that nation, not the people who license performances in London who deal with Great Britain and some other areas on the continent.

It may destroy the network of licensing organisations and companies that hinder distribution of material. Currently some material is not available in all markets because the local licensing hasn't been agreed. The artist and the publishers may be desperate to enter that market, but unless the local agent makes they deal, they are out of that market except via the "grey market".

It may not be, say, Universal Music withholding the license, it may be whoever holds the license for Universal Music properties in that country.

People wishing to perform certain famous musicals in France must negotiate with the rights holders in New York, as they are the "local" agents for that nation, not the people who license performances in London who deal with Great Britain and some other areas on the continent.

Why is this an "obstacle" for iTunes?

You misread the article. The current system is an obstacle. As you say, the proposed one would be much better (in theory).

As a professional musician, however, I think it's the absolute worst decision the EU has made so far (and they've made a lot), because the licensing rates will be drastically reduced for composers and lyricists

But I think there's two arguments here. I think the order itself is a valid and good order, for all involved. It is the associated licensing rates that you seem concerned with, and which should be argued about.

the major labels will still prevent Apple from offering DRM-free music... That also has an large negative effect on music sales...