Is Raspbian license as same as Debian license?
Debian as a whole doesn't have a license, individual peices of software in Debian do. Those peices of software do not change license because we recompiled them for raspbian.
Can I use Raspbian for commercial purposes?
Can I sell microSD card which installed Raspbian?
You can but if you want to be 100% compliant you need to be careful.
Speaking of the GPL specifically (one of the many licenses in Debian but by far the most likely one to trip people up, if you follow it's requirements you should be good for most other FOSS licenses) the FSFs interpretation of the GPL is it's not ok to link software that is under a license that is not GPL compatible against GPL software . Some dispute that position but following it is the safe option. So if you are writing GPL-incompatible software you need to be careful what libraries you use.
When distributing GPL software on physical media the GPL requires you to either provide the source code with the binaries or provide a written offer to provide it "on a medium customerally used for software interchange" at a price no more than the cost of performing the distribution.
If you want to go by the book you need to be very careful about distributing the source code for the exact versions of the software included in your image. I did write some tools to help with this see my post at viewtopic.php?f=66&t=89981&p=631147&hil ... er#p631147
but note that those tools only help for properly made Debian packages. Things like the raspberry pi foundation kernel will need seperate attention to collect the source.
Needless to say most SD card vendors don't bother collecting the source together and in practice they get away with it. Ss long as the source is publically available somewhere noone tends to care too much but there is always the risk of an author becoming litegous.
You also need to be aware that the raspberry pi foundation include various bits in their images that are under non-foss licenses. In particular the license for oracle java allows for desktop/server type applications but not for appliance type applications. The wolfram stuff is limited to non-commercial use only. I've no idea about sonic-pi. The firmware is restricted to use only on raspberry pi's.