If a baby is allowed to use a pacifier past age 1 then yes the pacifier could cause speech delays in children.
However it doesn't always happen to every child who uses a pacifier past age 1 as I know a 5 year old child who'm I babysit and he used to use a pacifier until age 4 and his speech hasn't been affected by pacifier use until he was age 4 when he finally gave the pacifier up himself.
Then again I babysit a 3 year old who uses a pacifier all day and he has speech problems and his mom said the doctor said that the speech delay problems were caused by the 3 year old using his pacifier for too long and that it needed to be taken away.
Although his mom still hasn't taken it away and is just waiting for him to give the pacifier up on his own but since he's having speech problems with the pacifier it should be taken away now to prevent any further problems and so his speech can be corrected.