The boot process is actually exactly the same in Yosemite. What was happening when you saw the spinning wheel in Mavericks is exactly the same as what's happening in Yosemite when you see the progress bar: the kernel is loaded, file system is checked, and certain system services are started.
But yes you're right -- the progress bar just makes it feel faster. It's an illusion.
No it makes me worry that somethings wrong with the filesystem and its rebuilding files to boot up. I'd like to see it go away.