I'm not surpised because as you and I know the font displayed to viewers must be in their operating system. I don't think that bloggers who are changing fonts are clear on that.
You may not like the fonts in your wordpress.com theme but it’s important to know that regardless of which fonts you may wish to choose to jazz up your blog with your browser and your visitors’ browsers can only use the fonts installed in the same computer. Obviously not every visitor to your blog will have the same fonts installed in their computers, so you can immediately see that problems will arise unless you choose to use common fonts.
If a reader does not have a specific font installed on his / her computer, the browser will determine which font is displayed. There are a very limited number of fonts (in English/Western languages) which are common for most operating systems/computers/browsers.