What's the point on phrase match for one word keywords?

I did it by mistake, see the strange results.

[fischermx]

Without realizing I entered some keywords with double quotes, i.e. phrase match for keywords already running on broad and exact match.
Anyway, does it make any sense to do this? I mean if it is just one word, what's the point on phrase match? Shouldn't be in this case phrase and exact match be equivalent?
So, I have this :
Keyword Bid Pos
Widget 0.24 3.1
"Widget" 0.24 2.3
[Widget] 0.24 5.4

I found the result a bit strange. Shouldn't be exact match more expensive? However, the same bid leads to a higher position for broad match instead.
And the phrase match, which I don't understand what does it mean in one word keyword, is surprisinly the one that leads to a better position!

[poster_boy]

In the case of one-word keywords, the broad match captures expansions or synonyms for the keyword while the phrase match captures queries with the keyword + additional words.