It's more like asking if there's a device I can plug my headphones into that will convert Spanish to English. That's just not going to happen. You could hire a person in the middle that translates from Spanish to English, but that is expensive and introduces a performance bottleneck.
Or, your analogy would be more accurate if you said a DVI to VGA adaptor. Yes, those exist, but only because the DVI spec ALSO sends the analog signals on a set of pins within the DVI connector. The adaptor just routes the existing signals to the correct VGA connector pins. Were it not for those pins, you would have to build a box to decode the DVI signal, re-encode them as a VGA signal, and output the new signal on the correct pins. And, of course, there's no way to convert a VGA to DVI signal using a cheap pin adaptor.
Those adaptors you see for five cents just convert the physical shape of the adaptors, and route the power and ground pins (so you could charge a Firewire device using the power pins off a USB connection). There's no way to convert the different data transfer protocols unless you introduce a black box with electronics in the middle.
