Actually, I’m wrong, you can display 3 at a time and it doesn’t have to be NIV
More than 3 versions can be opened side-by-side. I just opened 5 side-by-side for Matthew, verse 11:11 singularly, and for the entire chapter 11 also.
5 did seem to be the limit though, in side-by-side mode. The little "add parallel translation" button would disappear once the 5th parallel was added.
It can be a little difficult to choose which additional translation one desires once 3 or more are opened, since the scroll bar on the version identification box opening in drop-down menu disappears off the browser screen -- but the menu is still "scrollable" by highlighting the version which is lowest visible (WITHOUT clicking on a version) and using the mouse's scroll wheel, or by faking it by moving the mouse back and forth as in copying text larger than a combox opening, but accessible by scrolling in that manner.
There is also a feature when selecting single verses which says "...show all English translations", which results in top to bottom orientation of all the English translations they have http://www.biblegateway.com/verse/en/Matthew%2011:11 but not all in existence. As example; left out is NAB which can be found here --->http://old.usccb.org/nab/bible/index.shtml#acts.
NAB is not to be confused with NASB. The former is copyrighted, the latter is also, but has been made available to biblegateway for permitted or allowed use there. I get the impression that in regards to many copyrighted translations, copyright holders and publishers worry little about someone stealing the work from online source -- and printing it out. Others, for whatever reasons, want people to come to them...