95 S420 - brake lights only with engine running?

[sixto]

The bulb warning light went off in the S420 because a bulb is burned out. Nice to know the warning system works While diagnosing, it was a shock to my brake pedal applying recruit that the key has to be in run for the brake lights to come on. "Even my lowly Civic lets you check the brake lights with the key out," was her comment.

Unlike the SDL, the S420 lets you blow the horn with the key out so MB is creeping out of the dark ages.

What's the purpose of not having the brake light system energized all the time? Is it just to be able to fit the bulb warning feature?

ps - I get that deja vu feeling that I've asked this before.

Thanks,
Sixto
95 S420
87 300SDL