CentOS - Apr 2015 - Unexplained size difference with CentOS 7 (1503) -01 install media

In the process of updating my copy of the CentOS 7 (1503) -01 install 
media, I notice that it's ~70MB larger than the image that it's
replacing:

$ rsync mirrors.kernel.org::centos/7.1.1503/isos/x86_64/*DVD*.iso

-rw-r--r--  4310695936 2015/03/31 17:05:50 CentOS-7-x86_64-DVD-1503-01.iso
-rw-r--r--  4236247040 2015/03/28 12:15:26 CentOS-7-x86_64-DVD-1503.iso

But when I compare sizes using "du" on the mounted ISO files, I
can't
see any discernible difference:

Original CentOS 7 (1503) DVD:

$ du -ks /centos7/*
1    /centos7/CentOS_BuildTag
6148    /centos7/EFI
1    /centos7/EULA
18    /centos7/GPL
79428    /centos7/images
73378    /centos7/isolinux
281423    /centos7/LiveOS
3752743    /centos7/Packages
12696    /centos7/repodata
2    /centos7/RPM-GPG-KEY-CentOS-7
2    /centos7/RPM-GPG-KEY-CentOS-Testing-7
3    /centos7/TRANS.TBL

Revised CentOS 7 (1503) -01 DVD with centos-release fix:

$ du -ks /centos7-01/*
1    /centos7-01/CentOS_BuildTag
6148    /centos7-01/EFI
1    /centos7-01/EULA
18    /centos7-01/GPL
79428    /centos7-01/images
73378    /centos7-01/isolinux
281423    /centos7-01/LiveOS
3752745    /centos7-01/Packages
12696    /centos7-01/repodata
2    /centos7-01/RPM-GPG-KEY-CentOS-7
2    /centos7-01/RPM-GPG-KEY-CentOS-Testing-7
3    /centos7-01/TRANS.TBL

Seems like a large delta in ISO size for not much of a change in 
content.   Any ideas?

-Greg