Sony may not be selling as much content on PSN as Microsoft is on XBLA, but according to one developer it's not due to lack of effort or support.
Independent game studio Capy recently developed Critter Crunch for the PlayStation Network, a puzzle game where a cute creature eats and regurgitates other creatures to get them to drop jewels. There may have been a trailer at some point for the game that involved this creature puking out a rainbow, but you'll have to discover that for yourself.
In an interview with Gamasutra, Capy's Nathan Vella praised Sony for the company's support of indie development on the PlayStation Network. Not only does Sony provide a free-to-developers engine called PhyreEngine, but Vella says Sony "[supports] the living shit out of it, and they support it really well." Whenever Capy had a spot of trouble, Sony would fix the problem within a day, or directly send a member of support staff to Capy's aid.
Sony was also very respectful in Vella's opinion, saying "Sony treated us super well, respected us, and treated us like we weren't a small nobody developer from Toronto." Sony put Critter Crunch on the PlayStation Blog, on Pulse, and gave the game E3 support. Content is selling better on XBLA, but to Vella: "that's okay for us because they let us do what we wanted to do." Happiness is often more important than money, after all.
The PlayStation Network has a lot of unique content on it, so Capy's experience likely wasn't a one-off. Sony seems to want to make the PSN a reason to come to the PlayStation brand, similar to how one might buy a PS3 because it is also a Blu-ray player, or a PSP because it can play music and movies. I have really enjoyed some of the PSN's exclusive content, such as the PixelJunk series and games like Trash Panic, and hope Sony keeps this attitude in the future so we'll see more of it.