I thought I'd answer your question with a simple link, but the world is not that simple. The more I researched Apple's calendaring approach the odder it looks. The terminology doesn't help and large parts of Apple's documentation are outdated. [1]
Briefly, and I think correctly, Apple configured iCloud with 1-2 public calendars that any user can subscribe to, including US Holidays.
They didn't provide (or expose) the ability to subscribe to an arbitrary public calendar, such as the one for our mountain biking team that ends with the suffix .ics.
https://calendar.google.com/calendar/ical/highlandmtb%40gmail.com/public/basic.i cs
What's confusing (this is all very confusing) is that both iOS and OS X can subscribe to this URL. In theory (Calendar in Yosemite crashed when I tested) subscriptions in iOS and OS X do synchronize, presumably via iCloud. When you study the iOS configuration, however, these are setup as CalDAV calendars, not iCloud calendars. They don't show up in iCloud.com calendar view.
Practically speaking there are are a lot of public Google Calendars in the world, often for high school sports. These can't be seen on iCloud.com. In addition to this missing feature there's a bug. The above link is supposed to add the calendar as a CalDAV calendar to iOS; it doesn't actually work.
[1]
iCloud: Calendar sharing overview
iCloud: Share a calendar with others
http://www.imore.com/how-publicly-share-calendar-your-iphone-and-ipad
http://www.cnet.com/how-to/three-methods-for-sharing-an-icloud-calendar/