A professional manga translator weighs in.
Now, this is something I've noticed when looking at a lot of Yen Press manga. Things like Cage of Eden, Soul Eater and High School of the Dead. I don't know, maybe I just happened to grow up or get into manga at a time when a huge amount of effort was made into translating and relettering them -- all of the manga that I first read were always flipped, sound effects-ed, and written with literate quality English.
Viz seems to have stayed rather average, and quite above average with their releases of manga such as 20th Century Boys, but Yen Press's translations are internet scanlation quality. There was even a bubble where a character said "chivalry" and it had been left typoed as "chivarly". I can tolerate not seeing sound effects translated, but that is just very unprofessional.
That's why it's my policy for Yankee Goon Scans that we reletter sound effects and try to do a naturalistic dialogue style-- I'm just applying the standards that I was used to as a reader. It kind of pains me to see physical, hardcopy manga released by companies that are getting paid for their work, have such a slapdash level of quality.