To the contrary, they are an integral part of the living tradition of all schools of Buddhism, including the Theravada.
A ritual may be defined here as an outward act performed regularly and consistently in a context that confers upon it a religious significance not immediately evident in the act itself.
Because these practices form an intimate part of the religious life for the vast majority of devout Buddhist followers, they cannot be lightly dismissed as mere secondary appendages of a "pristine" canonical Buddhism.
Devotion being the intimate inner side of religious worship, it must have had a place in early Buddhism.
While the specific forms of ritual and ceremony in Sri Lankan popular Buddhism doubtlessly evolved over the centuries, it seems likely that this devotional approach to the Dhamma has its roots in lay Buddhist practice even during the time of the Buddha himself.
Certainly they would have done so shortly after the Parinibbana, as is amply demonstrated by the funeral rites themselves, according to the testimony of the Maha-parinibbana Sutta.
The Buddha also encouraged a devotional attitude when he recommended pilgrimages to the four places that can inspire a faithful devotee: the places where he was born, attained Enlightenment, preached the first sermon, and attained Parinibbana (D.ii,140).