Reading DRM'ed eBooks on an iPhone

There are many iPhone apps that let you upload files onto your iPhone for reading, usually via WiFi. They support any built in file format, so MP3 and MP4 audio files, PDFs, Word docs, Excel spreadsheets, etc.

Then there are many apps that let you read DRM'ed eBooks, such as:

• Kindle for iPhone
• txtr
• Stanza
  
• B&N eReader
  
• eBooks by Kobo
  

I'm sure there are more, now that there are 100,000 apps, it's getting hard to find all of the possibilities. "There's an app for that" should maybe become "There's a few dozen apps for that".

Here's the question: Why isn't there one app that combines file synchronization to a Mac or PC, a decent eReading experience and ePub DRM support? Bonus points for explaining why Adobe themselves wouldn't make an Adobe Digital Editions for iPhone (or is it a we can't have flash tit-for-tat situation?) I realize there's a lot of money in selling the books, but it's still frustrating for iPhone readers.