Postgresql's table & index compared to that of MySQL

For the same data set, with mostly text data, how does the data (table + index) size of Postgresql compared to that of
MySQL?

In this presentation, the largest blog site in Japan talked about their migration from Postgresql to MySQL. One of
theirreasons for moving away from Postgresql was that data size in Postgresql was too large (p. 12 & p. 41).
Specificallythey talked about index being 40% of total data size:  

http://www.scribd.com/doc/2569473/Migrating-from-PostgreSQL-to-MySQL-at-Cocolog-Japans-Largest-Blog-Community

Are there any reasons why table & index sizes of Postgresql should be larger than MySQL? Postgresql uses MVCC while
InnoDBdoes not use "full" MVCC, so perhaps that's a factor there. 

Does anyone have any actual experience about how the data sizes of Postgresql & MySQL compare to each other?

The company in the presentation used Postgresql 8.1. Has there been any significant changes in data size between 8.1
and8.4/9.0? 

Thanks.