I agree, there are times when you want to read the full article but think of all the other times you try to skim through a page and hit the back button after 30 seconds.
The initial concept will focus on HN articles because I read a lot of articles here and it's a great audience for feedback. Once I make sure the summaries are good, I'll expand to more news sources and build out the site.
A page or two later, and I'm usually done. Great things usually stay fairly sticky on the main page, and truly fantastic things will generally be mirrored elsewhere.
I've noticed that the goals of a startup-oriented aggregator do not always intersect my interests. I think cherry-picking out of the broader feed would only decrease the total number of items to read, but not necessarily improve the signal. The target audience (entrepreneurs, investors, startups) may benefit greatly; I don't know.
It's difficult to get a feel for how this works without some visible examples, though.