Aha, finally did find it. Indeed are different models.
Bush used a Prevost H3-45, while Obama is using a Prevost XLII
The Prevost XLII chassis – unlike the fiber composite bodied Prevost H3-45 incorporates a high tensile steel sub-frame and a stainless steel body and – as a consequence - is better suited to the type of protective modifications required by the US Secret Service. The XLII chassis is usually supplied with the DDEC VI Series 60 W/EGR 14L 515 HP engine coupled to an Allison World B500 6-speed automatic transmission.
http://www.examiner.com/rving-in-national/the-obama-presidential-bus-tour-another-win-for-prevost
Again, i'd say they're quite a bit different... in ways i didn't even notice.
http://www.prevostcar.com/cgi-bin/pages.cgi?page=xl2c
http://www.prevostcar.com/cgi-bin/pages.cgi?page=h345vip
They have full pictures you can view too and see the many differences.
Guess I have the better eye for buses... but I mean, from two pictures from the same angle, the differences are really striking.
