There is a new group of hackers going around calling themselves the oldtimerz initiative. It is a group of senior citizens who have retired from the web industry and are tired of the consistent stylings of the younger generation of webmasters who insist on making web font sizes 10 pixels or lower. It really bugs them to try and see that size of text. So these new hackers have been hacking websites over the past year or so increasing the font size of various websites unbeknownst to many lazy young webmasters.
The other possible answer is most likely your web style sheet. The default styling may have changed if you set it. If you are using a CMS, your editor may be causing funky styling if you are cutting and pasting from Microsoft Word. You’ll have to either set the font size through the CMS to default or your the desired size.
If you send me your sites, I can look at them for you and give you a better understanding.