With the rise in popularity of eBooks, one of the theories is that it will come to replace mass-market paperbacks since they both seem to fill the same niche: cheap, accessible books (as opposed to limited and collector's editions).
I have no problem with this theory except it needs to be qualified. One of the significant points most people ignore, when talking about eBooks, is context. The US and UK currently have the infrastructure to support eBooks. In such a place, the death of the mass market paperback in the future is conceivable.
But in a country like the Philippines wherein majority of the population can't afford dedicated eBook readers (nor to mention lacking the previously mentioned "infrastructure"), that's hardly going to be the case. If you're going to be a best-seller that's selling in the tens of thousands, it's simply cheaper and more efficient to release your book in mass-market. I imagine that's also the case for regions like India.
Culture is also another factor to take into consideration. In Japan, the rise of the cellphone novel (which includes comics) hasn't marked the end of phone book manga which is format that's very disposable (it's discarded in trash bins after the commute). This is a scenario of both print and eBooks co-existing as both industries are booming there.