@Westf: if it is open source it can be pirated. That is it can be used in other designs violating the license terms. Usually this is done by not making the derived work as open as the license terms require.
Branding it creates another possibility for piracy. Namely: the trademark can be pirated.
Why would anyone brand something that is easy to copy? In order to advertise it. Unless you brand it you can not advertise it. Hence branding helps to market your stuff and thus to collect more money as you otherwise could.
Is branding for open source stuff OK? I think so. If someone decides to open source his stuff, he is publishes all implementation details. Why should he not retain advantage like branding it? Have a look at Richard Stallman's opinion Why Open Source Misses the Point of Free Software - GNU Project - Free Software Foundation. I share his point on "free speech" vs. "free beer" although I do not share 100% of his views.
Udo