In the introduction of many Artscroll products the following is written, or something similar:
Transliteration presents a problem in all works of this sort. Ashkenazi, pure Sephardi, current Israeli, and generally accepted scholarly useages frequently diverge, and such familiar names as Isaac, Jacob, and Moses differs from them all. We have adopted a cross between the Sephardi and Ashkenazi transliterations, using Sephardi vowel and Ashkenazi pronunciations. Thus: Akeidas Yitzchak, rather than Akeidat Izhak or Akeidas Yitzchok. True, this blend may require some adjustment on the part of many readers, but it has proven successful.
Preface, pg xiv, Scherman, Nosson, 1993, Stone Edition Chumash (Brooklyn, New York, Mesorah Publicaitons, Ltd.)
What is Ashkenazi? While in general Jewish Hebrew pronunciation can be broken down into three major families (West, East and Yemenite) there is such divergences within each of these major families that its difficult to understand what was meant by Ashkenazi. My best guess is that it means the non-Chassidic American yeshiva dialect which developed in the 20th century. As for pure Sephardi, that seems meant to be juxtaposed against current Israeli since, at least in the popular conception, Israeli Hebrew is basically identical to the way Hebrew was pronounced by Middle Eastern Jews, popularly called Sephardim. And what are Ashkenazi pronunciations? I am pretty sure they mean Ashkenazi consonants.
Anecdotally I have heard people claim that they've heard people read Hebrew, while serving as shliach tzibur for example, with Artscroll havara, pronunciation. It sounds unbelievable to me, but the truth is that Artscroll has enabled Jews and non-Jews who knew very little about Judaism to pick themselves up by their bootstraps and encounter many classical texts and interpretations. Since I do not dispute the testimony of those who say they've heard people read Hebrew as per Artscroll transliteration, it seems they learned through this method which "has proven successful."
I don't know what yardstick was used to prove that it is successful (sales?). But given that Artscroll didn't experiment with a variety of methods at the outset it seems that it was an editorial decision from the start (the explanatory paragraph notwithstanding, I don't believe Artscroll ever contemplated either using Izhak or Yiṣḥāq instead of something more like Yitzchok or Yitzchak). The only explanation I can think of is that Artscroll didn't want to disenfranchise an entire market, people for whom standard Hebrew is Israeli pronunciation or a Sephardic variety, and certainly they wouldn't disenfranchise their own base. Thus, the compromise.
The Artscroll invention of a new way to read Hebrew has been criticized, and on good grounds if it is indeed propagating an artificial literary Hebrew among people, both for not being true to its own purported goal of representing Jewish tradition (ie, hypocricy) and for the misdeed itself.
However it is interesting to note that where it really counts, Artscroll's line of transliterated siddurim, prayer books, they use an entirely different transliteration method, as depicted below (click to enlarge):
While I can't imagine that the above transliteration scheme is not confusing, both to layman and to scholar--they simply invented a transliteration scheme that is neither intuitive nor scholarly--it very nearly does reproduce what I have called the non-Chassidic American yeshiva dialect which developed in the 20th century. Not only are קמצין rendered with /o/, but even the חולם, rendered with an /o/ as well gets some kind of diacritic which either means that it is supposed to be pronounced /oy/ or as the long /o/ of 'home.' If the latter, then Artscroll has, for some reason, chosen to use the non-Chassidic American dialect which developed in the 20th century, but not the yeshiva dialect. It is the one used in many American day schools as well as in many American Beis Yaakov schools (incidentally, the phenomenon of the two ways to pronounce Hebrew as taught to brothers and sisters needs some exploration!).
Paranthetically, Steg notes that "Whether they meant it too or not, Artscrollese is very similar to the Pre-Ashkenazic dialect." That statement needs some qualification, but it is indeed the case that the the proto-Ashkenazic pronunciation had some similarities to its Eastern sister dialect particularly in the area of vowels. It seems, from the evidence of early Ashkenazic manuscripts which confusingly mix qomatz and patahs liberally, like their Eastern counterparts, that the adoption of the Tiberian distinction between /o/ and /a/ came at a later stage.
There's even a Wiki entry on Artscroll transliteration.
What do you say?