That's true, that they get a lot of publicity for their apps, but that's not an accident: they have worked hard at building up their blog and no doubt paid DHH

That's true, that they get a lot of publicity for their apps, but that's not an accident: they have worked hard at building up their blog and no doubt paid DHH and others for spending their time on developing open source software. Clearly 37signals realise that marketing is important - and they are good at it.