Most browsers enable you to get a warning if you have HTTP content on an HTTPS page. This can be very annoying if you visit sites that mix HTTP content on their HTTPS pages. From your question it appears Wikipedia is one of those. When properly set, Firefox warns me visiting this page.
A web server is not required to offer HTTPS. Many sites do not offer HTTPS, and other may only use it to secure login screens and other content that they deem requires a secure path. Even if you use HTTPS, it is still possible to determine which servers you are browsing. In many cases the server only hosts one site, so the site would be known as well.
Until recently, the certificates required for HTTPS were quite expensive. Depending on the level of trust required, the cost is still high. Banks and other organizations which require a high degree of trust and security will pay high prices for their certificates.
If you wish to hide your traffic from local monitoring, you could use a secure path to a proxy. This may raise red flags with whoever is monitoring your traffic.
If you use a private proxy, anyone downstream of the proxy would be able to determine much of the information you are trying to hide.