Well, I think they would probably use different engines for the specific job needed. But I will say now, they most likely use a WHOLE server just for a MySql server and nothing else. If you are planing on making a database heavy application then you really must have the MySql server on a dedicated machine.
check out http://www.mysqlperformanceblog.com/ you will have to do some looking and some reading but provide a lot of really good information for performance tuning and/or what you can expect from both engines.
I've checked the link but I'm still confused.
I've googled this question a lot but there is no direct answer.
Everyone says that Myisam is good when you have read operations only or update operations only. and Innodb is used when you have a mix between read and update. but what if you have many read operations and some update operations? It's right that you have read operations more than update but still.