The unfortunate experience from RexPGP aside, yes, you can upgrade directly from 7.2 to 7.4; there is no need to stop in at 7.3.
Stick with 7.3r7. Two times I rolled to 7.4x code and both times my active sync connections went from 2000 constant concurrent to 500. My phones were spinning trying to connecty. JTAC states the VPN is fine.
2013-0520-0329: Active-Sync connection drop with 7.4R3.
here is what's in the relase notes but it doenst actually say if i have to go 7.2 > 7.3 to 7.4
of i can go to 7.4 from 7.2
Copyright © 2005 - 2013 Juniper Networks, Inc. 3 New Features in Release 7.4 R1 Please refer to the âWhatâs Newâ document on the software download site for details about new features. Please go to the support site http://www.juniper.net/support/downloads/group/?f=
o 7. 1R x
o 7.0R x
o 6.5R x
o 6.4R x
o 6.3R x
o 6.2R x
o 6.1R x