30 FOW 'suggestion' is
S.T.U.P.I.D. 
Seriously, what did people do previous to depth finders ? Did they mark their lines at 30 Feet so as not to harm the fish ? I think NOT...
What about ALL of the Fisherpeople that have
NO Depth Finder and have no intention of ever buying and/or using one ? What about people who fish off the Docks and such ? How the Hell would they have ANY clue as to the depth they are fishing at ? Anyone ever fished EAST of Saskatchewan for Walleye ? I've fished in Ontario and Quebec Lakes where we were lucky to
FIND 20 FOW less than 4 or 5 yards from shore ! What about fishing the Great Lakes ? How many Walleye photos have we seen with people using Downriggers !! "Dang, those poor fish !"
Although 'I think' the suggestion of fishing under 30 FOW for Walleye is asinine, I'm certainly not going to say that the 'Bladder Phenomenon' does not occur. I have seen and had it happen, but from my 38+ years of fishing, the ones that have issues with depth are normally the little guys under 2 lbs. The bigger fish are far better at 'self-regulation' of their bodily functions
in the short term. I've been far more worried about Bigger fighting fish hooked in 5 or 10 FOW than those 'Quick recovering' small guys at 40 FOW. The big fish will completely EXHAUST themselves whereas the little guys tend to have 'plenty of juice' at the surface. Either way, FISH in general are FAR, FAR more versatile than we give them credit. Besides, how many Walleye do WE ACTUALLY see floating around on the tops of Alberta waters ? Almost NIL. The FEW places where you'll find floating Eye's and Burbot are GUARANTEED to be from 'DEEP HOOKS' and/or poor Angling practice (Sylvan Lake Marina anyone ?)
So at what depth do I fish for Walleye ? Here in Alberta, normally at under 12' or 15' of water !
LOL....
I've caught some of my BEST Walleye in under 8 FOW when the water has been 74+ degrees ! I suppose If ALL you want to do is CHASE Walleye around all day, every day (like a SAWT Tourney, etc..) then yeah, you're going to have to find deeper water much of the time
For me, fishing is more about relaxing and 'hanging out'. I'm not interested in making it 'too difficult'
Anyway, JMHO.....
Cheers,
/FC....