s2member js & css files did not get gZipped

I have recently migrated a client’s site from a development server (on HostGator) onto Hostway which hosted my client’s live site.

But I notice a signification difference in speed on the two sites. I ran PageSpeed report (screen grabs below) on both sites, and see that some files are not being gZip from the site hosted on Hostway, while the other one did not have this problem.
(NOTE: the two reports shown on screen grabs below were ran at a time when the two sites were identical in every ways)

Report on dev site on HostGator:

Report on live site on Hostway:

As you can see on the screen grabs, 2 of the 4 files that did not get gZipped were generated by the s2member plugins. To help with the load speed of the site, I have temporarily deactivate the script that generate those files, but the site will need them to be running properly as it expanses to include other content, so I am hoping you can help solve the mystery as to why these files can be gZipped on HostGator but not on Hostway.

(I have of course, contacted Hostway, and… as predicted, they told me it is the plugin’s problem, which I don’t buy… but I thought you guys will be more willing to help me figure this out… :-) )

Thank you much