Depends on who you want to be able to access your site. Not everyone had 10Mbps+
And if you're really targeting people that have trouble loading such a font file, then you have much, much bigger problems than centering things (you basically cannot put any image on your website).
Where's that ratio coming from? Shipping fonts is just good practice when you want your website to look consistently on all platform, it doesn't mean anything else about how the website is made.
Also, 100kbps is a very slow connection, it's 2 orders of magnitude less than the 10Mbps you talked about earlier, and when you have this kind of very poor connection everything is kind of slow anyway (even the very barebone HN's front page is 120kb!).