ls -l /bin/sh
The output would be some thing like this
lrwxrwxrwx 1 root root 4 2010-07-22 01:20 /bin/sh -> dash
If you look at it, you will realize that /bin/sh is actually a symbolic link to dash.
Now if you are familiar with shells then the first thought that would come to your mind is, shouldn't it be bash ?.
Well no its not a typo by ubuntu, it is actually dash which actually stands for Debian Almquist Shell.
This change was done not because the default bash does not have the features required, but because the bash is too big and the number of shell instances that are started during the boot process makes the size of the bash as a disadvantage.
To counters this and make the booting quicker a quicker lighter version was made and called dash.
Now to change all the sh to dash in all the boot scripts would not have been very advisable so instead the usual /bin/sh was changed to dash by placing a symbolic link to dash.