1) Yes, only some investors.
2) The difference is the same between the present tense and present
continuous tense (even if a "should" is included which is a modal
showing obligation). Read your books or do some searches here on:
present continuous
(top right Search corner)
or click on the relevant buttons underneath your original posting.
In case of idioms, suggest searching at Yahoo with:
"flex one's muscle" dictionary
(commas are important to group up terms)
and you will find appropriate dictionary pages definining the idioms
including the page at "flex" of this dictionary:
http://www.m-w.com/dictionary/flex