Regardless of demand, they're (apparently) not keeping the retail chains up to speed, nor supplying them suitably when stock does become available. Even if they don't have much stock to offer, they can tell the retail chains a timetable of supply. Amount of stock and demand should have no affect on logistics - only delivery times.
Why's "supply issue" in quotes? It is a supply issue. Sony launched with enough supply to keep early adopters happy. If they had released 4 months earlier with 200,000 units for Europe, you'd have stories of sell-outs and PS3 being unable to find anywhere for 3 months. Sony chose not to go this route. They choose to enter the market with significant stock. For some people that's a better choice - they could be sure to get a PS3 if they wanted one, rather than having to keep popping into shops and ringing round stores to find if anyone had any in stock (though in Sony's case, thanks to a well managed supply chain, it seems you'd be able to reserve one with some certainty when you'd get it. That wouldn't be an option with a poorly managed supply chain). It also killed any eBay entrepreneurs. For other people, Sony's choice was a bad one, making the EU wait longer and so some people who would have bought early on had too much wait. And the entrepreneurs missed the chance to resell their PS3 for a hefty markup.