Yeah, but you gotta understand. Without Sun there's just IBM. There's no other vendor in the mainframe business, which is still big business. You don't think the IRS has time or money to manage the size of cluster they would need to operate effectively? So they rely on big iron, which is reliable and redundant and engineered to be that way over 40-50 years of experience. Clusters are garbage compared to a real mainframe. Sure, you have distributed filesystems now, and you can sort of split CPU around, there's management systems, etc, but all of this are ideas that come straight from the mainframe os which does all this "by itself". Google managed to make a pretty cool mainframe from commodity hardware but whatever.
Now, if you're not going to go with IBM for your database, you're probably going to go Oracle. But if you need big iron to run this huge database, you're going to have to go with IBM with z/OS and linux virtual machines or something. Oracle now has viable, proven mainframe line and all they have to do is throw money at it. They'll just move to selling complete packages instead of just DB at the mainframe level. With all this "cloud" bullshit (eg "Mainframe on the internet"), big businesses are interested in managed services and Mainframes have always been vendor managed.
Even IBM minis like AS/400 boxes come with full support from IBM. They monitor the box 24/7. I used to operate them long ago, and I remember that a disk went bad in one of our storage boxes (they had these giant enclosures with over 100 disks in them). Literally the message flashed on my console "SYS01281: DISK ERROR" blah blah blah and I turned around to get the binder to figure out what I had to do. By the time I turned back to my desk my phone was ringing and it was IBM support letting me know a tech would be there within 4 hours to replace the drive. Awesome.
So like, Sun/Oracle can do the same thing, and they can compete if they play their cards right. Oracle has poached a lot of high-end people from IBM in the past so this was only a matter of time.
Regarding MySql: MySql is a toy. Go to where the money is and you will find mainframes still. No one in their right mind would put anything important on MySql. Yeah yeah, facebook pft. If Facebook was making more than a few mil they would switch. Internet hits != money. (I'm talking Fortune 25 money, government money, world organization money, casino money, bank money). So I, for one, welcome Oracle and Sun back to this venue.