How exactly does a conference abstract differ from an article abstract? I am currently taking a brief course in Technical/Academic Writing. At one point, in passing, the lecturer (who's a researcher in linguistics himself) mentioned that one should not confuse a conference abstract with an article abstract, with the exact phrasing "... that's a whole different story." 

Unfortunately, at that moment in time I did not reflect on what those differences might be, but now I am writing a conference abstract I realize that I have never really paid much attention to the fact that I am not writing to a journal. Besides the fact that a conference abstract is preamble to a primarily spoken form presentation (poster/oral) instead of a written one, I don't really see why it would be "a whole different story". 

Assuming that there are no differences in requirements and limitations, what are the fundamental differences, between a conference abstract and an article abstract, that one should be aware of?

PS: if it matters, the field I'm mostly concerned about is medical research
To me an article abstract summarizes the entire article including the overarching questions through methods, results to the major conclusions. 

A conference abstract will of course also summarize whatever is presented at the conference. The differences lie in several aspects of variable weight:


Conferences are often focused on a specific topic so one can be less stringent with the background
Conference presentations may involve work in progress and as such the final conclusions maybe quite hazy.
The conference abstract may be written before most of the work has actually been done (this is quite common with some conferences in my field) and becomes an "advertisement" for what might come.
The conference contribution may in some cases involve a paper but can also be a poster or an oral presentation. depending on which abstracts may contain varying levels of finalized conclusions.