There's a certain voice we all have a tendency to use when a pet is around-dog or cat. It's that same higher-pitched and coddling voice we use when talking to babies or really almost anything we consider cute. The reaction is near automatic, as we can observe in many movies, where as soon as a lonely main character acquires a pet, they are swarmed with people cooing for the affection of the animal. Some of us also carry normal conversations with our pet, or make blithe commentary towards them as if they can understand. The upside? This is completely normal. Almost everyone does it -after all, isn't it nicer to imagine you can explain whys and wherefores to a dog? No one suffers for the behavior unless this habit is accompanied by a neglect towards human interaction, so nothing needs to be done to adjust it. But one of the neat things scientists have been looking into is how pets respond to this dog-speak, and how we perceive their reactions.
Dogs are much much better at reading body language than the average bear. They don't, unfortunately, understand the specifics of why you had an awful day as you explain it to them, but they sense the distress and by our mutual relationship with pets, want to comfort us. Puppy-voice also serves a purpose when talking to, well, puppies. Dogs respond to the tones in our voices and when we use that high pitched voice it invites puppies to play. Adult dogs notice it, but don't find the voice itself (at least disembodied) all that engaging. So go ahead and continue to talk to younger dogs as you always have, but keep in mind you might want to try something else for the adults to engage them more at their level.