Actually, I think you are wrong. The biggest problem I think with Mini's is not the platforms their aimed at, or competition with the big retail games. I don't own a PSP, but I imagine they would be fantastic for playing on the bus, for instance. I think the biggest problem is that there is no way to try them out. Before you buy your first Mini, there is no way of knowing whether you going to get something comparable to a PS1 classic, or a flash game on miniclip. A simple 1 hour trial, or first level demo of these titles would have helped considerably in my opinion. Especially when WipeoutHD costs little more than 2 of these games.
There is also the price issue. I would have been incredibly disappointed to have paid for Fieldrunners (OK, yes I did pay for it as part of PSN+, but thats besdies the point). I love it, brilliant little game. But in reality not really any different to the hundreds of other tower defence games out there, many of which are free.
Warning: Dig at Apple fans coming up.
Ultimatly sales and adoption figures show that the types of sheep buying Apples iphone over and over again, not only do they have to hold their phones diffrently, but they are willing to pay £2.99 for an "app" that puts a green JPEG on screen and makes a whooosh sound whenever you use the phone. Perhaps the people buying Sony's products are not under the curse of Apple so much that they feel compelled to spend hundreds of pounds a month on micro-transactions just to turn on the LED on the back of their phone.