You are using fonts not installed on most machines and it appears you are only providing a .ttf version. IE needs .eot files and ignores .ttf. All of the other browsers use .ttf in the most recent versions.
Also keep in mind that older browsers may not see it at all.
I never download the actual font file from google fonts, I always use their "Quick-Use" link and the "Standard" code that gives the link for the <head> of my site. Google's downtime is far less than my current hosting servers, so I don't mind leaving the font on their servers.
That being said, I just went in and used the "Download your collection" link and it looks like they only give you a .ttf.
I'm not seeing any kind of option for additional versions, I'm guessing it's a licensing restriction.
A ttf webfont won't display in IE last time I checked. Need an eot or woff for that. I wonder if Google is doing some sort of manipulation to force you to use their script? And after reading into their docs it appears that is the case:
In www.google.com/webfonts you can add a specific font family to your collection, and then in the top right click 'download collection' to download the binary TTF files. This is useful for making web page mock ups, or otherwise using the fonts. - From - http://code.google.com/p/googlefontdirectory/
It appears they give you a ttf to use the font on your end instead of distributing all of the formats. This could easily be due to licensing as Jon eluded to. For reference the Lato font is available at FontSquirrel as a kit but the other font is not available from what I can tell.
In my experience many Google Web Fonts are not 100% cross browser compatible because they lack all the supporting file types (eot, ttf, svg & woff).
In my opinion, Adobe TypeKit is more reliable and they have a nicer library of licensed web fonts.
I second Nancy's suggestion, though here's what I have been telling my clients for years about fonts:
Type on the Web is very limited. You have three. That's it. End of story. Here's the three:
San-serif, like Arial or Helvetica.
Serif, like Times
Monospaced, like Courier.
Within those limitations, there is a little variety, but not much. Fine typography just doesn't exist, unless you do something as an image. Drop shadows, forget them. In fact bold and italics don't always work. Also, any attempt you make to define the size of your typeface may be overridden by the "client," which is whatever browser the goofball viewing your page is using in the moment. In fact. some computers cannot display any typefaces at all because they're using a character-based browser, like Lynx. (Remember the Internet before there were pretty pictures?)
That said, any attempt at doing font work on the worldwide web with .WOFF, .TTF, .SVG or .EOT is fraught with peril. You're always going to find someone with an antedeluvian browser that cannot display the typeface. Also there are still people using Microsoft's browsers, the latest of which is still proving that Microsoft will steadfastedly go its own way and ignore the rest of the community when it comes to creating browsers. They're ticked off, because everyone is using Webkit "Touch Events" calls for touch screens instead of their own technologies, called "Pointer Events." The article I linked to was published ONE WEEK after Microsoft finally released Internet Exploder 10.
Getting back to type, one of the main difficulties with any typeface on the web is the general nature of the web. The worldwide web standard for display is 72 DPI. Now, while rendered type is rendered by the browser's rendering engine, one's screen is generally 72 (or in the case of Apple displays, 96) DPI. Newsprint is 300. Books are 1200 or more. So, your type may be absolutely beautiful, but its beauty may well be lost on the screen, as the human eye will simply scan past it.
People do not read websites. They scan them. So, if you have text, you should be paying attention to breaking it up into small chunks that won't tire the eye at 72 DPI. Sweating small stuff, like typefaces that don't come with all computers and all browsers is something you ought not find yourself pondering for more than a couple of minutes.
If my client wants a particular typeface that I can set up for them using Google or Adobe or someone else, I'm happy to do that. But it does not bother me at all to see it not supported. Heck, line breaks don't even match from browser to browser! Why am I sweating type?
<Also there are still people using Microsoft's browsers>
It may surprise you to know that IE4 was the first browser to support embedded open type fonts (.eot). It wasn't until much later that the other browsers came on board by supporting other proprietary font flavors (.ttf, woff, svg, and others...).
AFAIK, .eot is still supported by all versions of Internet Explorer.