Floating tables in Word 2013 will not extend beyond the margin at the bottom of the page

If you want some particular text to appear in the footer of only the last page of a document, you could use the following field construction

{ IF { PAGE } = { NUMPAGES } "The particular text for the last page only"  "Text for other pages" }

In place of the "Text for other pages" you could just use "" of nothing at all, if there is nothing to appear on the other pages.

You must use CTRL+F9 to insert each pair of field delimiters { } and you use ALT+F9 to toggle off their display.

Doug has given you a better solution for having a different footer on the last page, but, to answer your question, yes, this is a change in Word 2013. It's not just tables: it applies to wrapped objects generally. Here's an official explanation from MS:

Figures that have text wrapping applied, but are on the same plane as the text, are no longer allowed to bleed into the top or bottom margins.  You can still position a figure in the top or bottom margin without moving the anchor there if the figure is either above the text or below the text.

There were a couple reasons for the change:

• Conceptually, the idea that a figure is on the same plane as the text implies that it should be treated as a part of the flow of the text.  Text isn’t allowed to spill over into the top or bottom margin, so we’ve started applying the same rules to figures as well.
• More specifically, by changing the behavior, we were addressing cases in which figures could get inadvertently pushed down into the bottom margin as text was added above the anchor. This would cause figures to overlap footers and footnotes as well as cases where figures would collide with other figures on the page.

What this means in practice is that objects with In Front of Text or Behind Text wrapping can extend into margins; those with Square, Tight, Top and Bottom, etc., cannot. Since a wrapped table basically has Square wrapping, that eliminates it.