Yes, the incidences of CVST following vaccination with the J&J vaccine and the AstraZeneca vaccine are higher than the background incidence of CVST.
For the Johnson and Johnson vaccine: Between March 19 and April 12, 6 cases of CVST with thrombocytopenia were reported to the Vaccine Adverse Event Reporting System (VAERS),1 a database maintained by the CDC and FDA. These 6 cases, all in women under 50, were what triggered the joint CDC and FDA recommendation on April 13 to pause vaccinations with the J&J vaccine.
An April 14 CDC presentation (a day after the federally-recommended pause) stated that, among women 20-50 years old, the observed CVST cases exceeded the expected background rate by "3-fold or greater." (Slide 24)
At the time, 6.86 million J&J vaccine doses had been administered, 1.4 million of which had been in women 20-50 years old. This is 0.87 cases of CVST with thrombocytopenia per million J&J vaccine doses administered, or 4.3 cases per million J&J vaccine doses administered in women 20-50.
Since the initial 6 reports, the CDC has confirmed 14 cases of CVST with thrombocytopenia as of April 25 (very recent April 30 article). By April 25, 8.1 million J&J vaccine doses had been administered. This is 1.7 cases of CVST with thrombocytopenia per million J&J vaccine doses administered. (The statistics for women 20-50 alone are not available.)
Going into the mathematics:
A Johns Hopkins page states CVST "affects about 5 people in 1 million each year." This means in 2 weeks, CVST affects 0.19 people per million. Out of 8.1 million doses administered, we would expect to see 1.55 CVST cases. The 14 cases reported to VAERS and confirmed by the CDC is close to 9 times the background rate of CVST.
For the AstraZeneca vaccine: On April 7, the European Medicines Agency (EMA)2 wrote:
As of 4 April 2021, a total of 169 cases of CVST and 53 cases of splanchnic vein thrombosis were reported to EudraVigilance. Around 34 million people had been vaccinated in the EEA and UK by this date.
This is somewhere between 2.5 to 5 cases of CVST per million AstraZeneca doses.3 (I am unsure where the question's figure of 72 cases in 80 million vaccinations came from.)
Going into the mathematics:
Using the same rate of 5 CVST cases per million people each year, we would expect to see anywhere between 6.54 and 13.08 cases out of 34 million people vaccinated (depending on how many had received one or two doses). The 169 cases reported to EudraVigilance exceeds both figures and is between 13 to 25.8 times the background rate of CVST.
1 The caveat with all VAERS reporting is reports do not mean a vaccine caused an adverse event.
2 You can think of them as the EU equivalent of the US FDA.
3 Unlike the J&J vaccine, the AstraZeneca vaccine requires 2 doses. It's unclear how many doses of the AstraZeneca vaccine had been administered by April 4, only that 34 million people had been vaccinated.