Hadoop is a batch oriented so discussing it in terms of messages isn't really applicable. Hadoop works on a pool of data a batch at a time.
Storm is a stream processing system that operates on a stream of data, one message at a time.
With Hadoop, you want be able to extract any answers from your data until the batch is processed. Imagine for example the case of twitter's trending topics:
With Hadoop, you could take all of the tweets from the last 30 minutes and process them looking for trending topics. That 30 minutes of tweets is your batch.
With Storm, you can act on those tweets as a stream of data and start immediately detecting trending topics as you are working with the stream in real time rather than
as a batch.
So Hadoop is not real time. It doesn't operate on messages so guaranteeing messages are processed doesn't apply.
We included reliably in the summary because, Hadoop v1 had numerous reliability issues. Hadoop v2 addresses most of those, however, at this time, most people
equate Hadoop reliability with v1.