I think the design differences lean more towards max temperature exposure and nominal temp range. Meat probes being designed to withstand a max of around 350* or less, and the average user having a nominal range of 135-205*. Some pit probes are designed to withstand up to 550* (or more), with the average user having a nominal temp range of 200-300*. Of course, there will be variations with each brand and they will be listed as such.
For low & slow cooking I've never had a problem with a meat probe for monitoring grate temps, up to around 275*. I would never attempt the use of a meat probe for monitoring temps in my kettle with a 475-500* rotisserie cook spinning away, though. Since I've had them, I always used my pit probes instead of a meat probe for chamber/grate temp monitoring. Accuracy not being the issue, but concerns of damaging a probe with high heat exposure.
Eric