That's completely the other way around and soothsaying :) BSH is a separate entity created 60 years ago by both companies but now fully owned by Bosch.
Bosch and Siemens had a joint venture since like 1960's. Around a decade ago Siemens sold out their BSH part of the company to Bosch completely and Bosch still makes some equipment under that brand. Yet still Siemens exist and is completely independent company.
Such joint ventures were not unlikely events for companies in that space in Europe. Siemens had parts of the company separated more often. Nokia Siemens Networks is kind of big (they ditched the Siemens name a decade ago), Nokia Siemens had briefly been know for cell phones for instance, Fujitsu Siemens did IT Enterprise hardware and software, PDAs and similar (here Fujitsu also took over and ditched Siemens part of the name).
Your buying advice ain't better than the guy's that sold that dishwasher to Jeff.
I have clearly been misinformed then. Though it kind of made sense to me on the surface, because it was hard to fathom why Bosch would tarnish its reputation with such anti-consumer products, whilst leaving the Siemens brand with the less hostile variants.