You have the wrong approach sorry
I have to say that this is totally not on. No one can take a sample of 500 hundred apps and as a result of your personal testing and your opinion come up and say based on this and my results then this percentage of total apps available is junk.... I am sorry but your calculation is incorrect. I have 250 Apps and out of that selection less than 5% of my purchases I have been unhappy with. I received credit for 9 purchases from Apple from apple as they either did crash or did not offer what they advertised and the rest I wrote off. When one purchase an Application they do for a reason, this is based on what they desire some like comics , some like books, many like games a lot do not want to pay so they down load free stuff, some need business solutions other music or may be education apps and many many more. One cannot bundle all these users in to one group. I own 30 cooking books or apps and all are excellent I surveyed various web sites and reviews before buying. with exeption of a copy of a web site app every one is great and I personally have cooked recipes from all the apps. Based on that. It is 99% of what I purchase. my point is that no one can state that 90% of all apps in Apple's iTunes store are crap based on a small survey it is simple as that. I suggest you enjoy what you like and do not get hung up on statistics because at the end of the day you miss out on the real experience that every one enjoys with the iPad.....
Oh one more thing like Sweet poison I also use the Internet a lot daily and I also use a variety of apps to gain knowledge on subjects that are relevant to both this forum and iPhone forums where I Moderate. Considering the number of sites involved and the variety Of information I access, not once have I had issues with accessing any one of them.