Hubo vs. había

Hubo vs. había
 

Two sentences in an article from Agencia EFE that I just read are puzzling me:

"Durante décadas hubo congresos internacionales y asociaciones profesionales dedicadas a la eugenesia..."

"Más de 65.000 personas fueron esterilizadas a la fuerza o por engaño en Estados Unidos bajo los programas de eugenesia en los 33 estados donde hubo leyes que permitían esas prácticas."

It seems to me that, in both of these sentences, the most basic rules for selecting between the preterite and the imperfect would rule out using "hubo." Furthermore, my understanding was that "haber" in the past even takes the imperfect (había) in contexts that, with other verbs, would normally require the preterite. I thought the preterite of "haber" was pretty much reserved for expressing things like "Hubo un incendio," "Hubo una boda," etc.

Perhaps this usage has something to do with journalistic style?

"Hubo congresos" is correct, since they're setting a temporary frame "durante décadas".

And although "había leyes" would have sounded a little better, "hubo leyes" stresses that those laws don't exist anymore (and maybe that they didn't exist for long).