In a comment, Scott pointed out that Dr. Dobb's probably has a higher “ad ratio” (advertising space as a percent of total pages printed) than SD Times. I would think so, but it's not necessarily a good measure of magazine success. Pardon the return to days of yore when I was in publishing...
Anyway, ad ratios are controlled by adjusting the number of pages in the magazine. Back in the late 80s, Dr. Dobb's and Computer Language ran well over a hundred pages every month at ad ratios of 40-50% (IIRC). I think Computer Language's biggest issue was 160 pages and I'm going to guess that Dobb's went over 200 on occasion.
But... Computer Language was much more profitable. Dobb's had a bigger and better paid staff while at Computer Language we had a small staff of people in their mid-20s. Miller Freeman was known in the trade as the place that paid terribly and worked the hell out the staff but had tremendous opportunities (I was hired as Technical Editor of Computer Language when I was a 25-year-old and became Editor-in-Chief less than a year later). Our group did so well in the market that Miller Freeman bought M&T Publishing, the publisher of Dr. Dobb's. (And then, in classic “it's nothing personal, it's business,“ fashion, they gave Dobb's the entire subscription base of Computer Language to boost its circulation. Thirteen years later and I'm still pissed off about it. 60,000 people who paid to read my magazine got Dobb's instead. Oh, and a subscription form for a new magazine called Software Development “from the team that brought you Computer Language.“)
You also can't judge a magazine's editorial success by circulation numbers, since circulation is essentially bought. Back in the early 90s, it cost about \\(30 in marketing to get a new paid subscriber (at a subscription rate of \\)24 or less!). For “controlled circulation“ magazines (those for which you fill out a form to receive a free subscription) circulation is, of course, even more easily controlled by marketing decisions.
If you want to judge a magazine's editorial success, the number to know is the resubscription rate, which represents a positive judgment of editorial quality (especially in a paid circulation magazine). Of course, that rate is a carefully guarded secret!