There is a very simple reason for the lack of a resize handle on your current drive. Notice, in your screen shot, that in the left hand pane you have a disk labelled "Macintosh HD" which also has a volume labelled "Macintosh HD". With the disk highlighted, look at the bottom of the window and you can see that the disk is of the type "Logical Volume Group".
Now, if we look at @tubedogg's screenshots, in the left hand pane we can see the serial and make of his hard drive (a 1TB Western Digital HDD) which has a volume labelled "Ted" (I'm going off the top-most drive here). The bottom of the window tells us that the drive is an independent drive connected internally via SATA. Perhaps you can already see where I am going with this?
@qmlowery, it seems that you have a Fusion drive, and not a typical HDD layout, am I correct? If not, you say that you recently reformatted, so I'm guessing you created a Core Storage volume on your disk. These act differently to regularly connected drives. Imagine, if you will, that there was a resize handle for your Fusion Drive. You drag the handle to create 20GB of free space (in which you could put another partition or something). Where is that 20GB of free space located? On the 32GB of Solid State storage? Or on the remaining space which is conventional storage?
For this reason, resizing is not available on a logical volume group. OS X wouldn't know where to cut out the free space. In order to install your linux partition, you will need to ignore the steps that tell you to resize the partition, and instead just create a partition of the specified size using the "+" button.
Hope this clarifies things for you and helps you out. :)
Source: My time fixing custom Fusion Drives at an AASP. :P
EDIT: There's a lovely in-depth article on CoreStorage here.