It is rarely both. Let’s take CNN.com as an example. I don’t think I need to explain how large of an audience they reach through their website.
When I visited their site from my iPhone 5S, which was connected via WIFI to my home Internet (50 Mbps from Cox), it took 4 seconds until anything showed up on my screen, and 10 seconds before the entire webpage loaded. It loaded an astonishing 2.1MB of data just for the home page. Which bloated to almost 3MB without performing a single action on the website, just waiting for 30 seconds after the webpage loaded on my iPhone. The difference between their desktop website and their mobile website, is a mere 40KB which is a 2% difference.
What does this mean?
CNN basically thinks your 3G/4G connection is just as powerful as your home wifi connection. I don’t need to tell you that this is far from the case. I wish it wasn’t, but it is. Using this website while on 3G/4G just isn’t feasible if you are the least bit impatient. In my case, my home Internet is almost 25 times faster than my cellular connection.
I could redo CNN’s entire home page with 90% of the functionality at less than 1/5 its current size. And I would venture to guess few would miss the last 10%.
The point here is, CNN’s mobile webpage looks great when it is fully loaded. But in the real world, with our current cellular speeds, it just simply isn’t practical.
There is no reason a mobile website should be over 500KB in size, even for CNN.com. Including images!
If CNN was using WordPress, they could install the WP Mobile Detector, and get a mobile website that is less than 500KB in size. Even with all of the short comings of WordPress, they would still be better off for the majority of their mobile website visitors than they are now.
If you’re wondering how your mobile website stacks up against your desktop website, checkout this tool I created a while back that does just that. It analyzes your complete website and gives feedback right in the browser.