They fraudulently make the claim "lots of people like this". User's believe a "most downloaded" means other people like them have made a decision and picked this little grain of wheat from the chaff.
Bot farming is fundamentally lying to your potential customers to the detriment of applications that should be on the list.
Why aren't people rallying against Tapjoy when they're incentivizing people to download apps in exchange for virtual currency? As long as you pay $20-30k, you have enough downloads to breach the top 25.
Or take banner ads. Zynga has the ability to throw $100k IOs at random ad networks and their new apps are instantly in the Top 25 shortly after launch. Does this reflect popularity/quality or is it just a competition between who has the biggest wallet?
If Apple changed it's app store algorithm to function like the Android app store (that takes uninstall rates/ratings into account), this wouldn't be a problem.