Oracle is a less expensive RHEL,
No, Oracle rips off RHEL just like CentOS SL and others do, but Oracle doesn't add value to RHEL, instead they compete with RedHat and with less expensive you get a fourth party to the sources (after they have gone through the original project, then Fedora, then RHEL) trying to provide support for something they only cloned off of someone else, whereas RedHat are pretty much 2nd party to the sources and have a lot more knowledge on them, so you get what you pay for in terms of support or with Oracle even less than what you paid for.
Cent tends to lack security updates after RHEL releases,
CentOS has been pretty onto it as of late, 6.5 only took about a week after RedHat released (iirc) and they are very quick on updates, usually the same or next day. Also now that the devs are getting paid (by RedHat) for their time it should be even faster.
Scientific is dependent on government funding but gets security updates in what could be called a timely manner compared to Cent.
There have been times that SL has beaten CentOS and times that CentOS has beaten SL.
If this means Cent gets security updates in a timely manner after RHEL version bumps then it is a good thing.
My understanding form the original CentOS announcement is that CentOS will still have to build their own binaries from the publicly available sources (RedHAT won't allow them to use RHEL binaries) so that part won't change, but as I said above, the devs are now paid for their time which will make a huge difference, plus I imagine that they will have better access to RedHat for issues with rebuilding the sources. RHEL is not self-building and as such has always had difficulties trying to get it to build, especially after a new major release. Often times you can look at the sources and wonder how RedHat managed to get it to build. Now they should have better access to get help with these issues instead of having to figure it out for themselves.