Graphite vs. Prometheus storage comparison is confusing

In https://prometheus.io/docs/introduction/comparison/ under the Graphite section there is, to me, conflicting and confusing information that I can't make sense out of. I have bold italicized what I think the conflicting information is. Why is Prometheus unsuitable for historical data long term? It says Prometheus data may be kept arbitrarily long.

Storage

Graphite stores time series data on local disk in the Whisper format, an RRD-style database that expects samples to arrive at regular intervals. Every time series is stored in a separate file, and new samples overwrite old ones after a certain amount of time.

Prometheus also creates one local file per time series, but allows storing samples at arbitrary intervals as scrapes or rule evaluations occur. Since new samples are simply appended, old data may be kept arbitrarily long. Prometheus also works well for many short-lived, frequently changing sets of time series.

Summary

Prometheus offers a richer data model and query language, in addition to being easier to run and integrate into your environment. If you want a clustered solution that can hold historical data long term, Graphite may be a better choice.

Start with the Graphite section of the comparison page at https://prometheus.io/docs/introduction/comparison/, especially the Storage and Summary sections quoted in the issue. Determine how arbitrary local retention differs from a clustered solution for long-term historical data, then revise the wording so the distinction is unambiguous; done when the two statements no longer appear contradictory.