Regardless, I wouldn't really count a laptop as an instrument in itself (unless you are hitting it or something) but more as an apparatus for controlling software instruments (synthesizers, samplers, etc.). In some regards, this makes it similar to an organ console, or the keyboard part of a piano, but considering that it can be used for controlling a vast array of very different software instruments, and being far more multi-purpose, I would at most consider the laptop (and all computers in general) more of a component of software instruments, rather than an instrument in itself.
The turntables however I think more easily fit into the category of instrument. They are a unique anomaly (similarly to radios and tape-recorders, and samplers) in that they do not generate sounds on their own but rely on the imput of recorded sounds to make music with them. However, turntables are capable of producing unique sounds via their manipulation of recordings that can be very beautiful and ripe for exploitation by imaginative composers. I think it is silly to argue that turntables used in this manner aren't instruments. Radios are a little more vague, because they basically only operate in chance. You can control volume, and what frequency is being recieved, but what comes through is ultimately out of the musician's control. Still, these mostly uncontrollable sounds can still be utilized in musical composition (as has been done by John Cage and others). Really, if it makes a sound, you can use it in a composition. Some things are designed specifically for that, others are found to have interesting properties or are capable of generating unique and interesting sounds and are thus appropriated as instruments. Most of the intentionally built instruments we have today were likely developed from appropriating found objects a long time ago, so is it really so absurd?
Welcome to planet use your imagination a little bit. Think outside the sound box.
EDIT: Also, going back to the musical saw. No, it wasn't originally a saw without teeth. That is a pretty recent developement. When the saw was first utilized for musical purposes, it was a found object, not made for that purpose. People noticed (probably by accident) that it could make neat noises, and some experimented with it and developed skill and technique, and could perform music with it. The saws that are made nowadays specifically for music making are descended from just using a normal "non-musical" tool as a musical instrument. You can still play a regular saw, with the teeth and everything, and that still makes it an instrument for making music.