That statement is not generally true. Most DVI ports on video cards are
DVI-I ports. That means that they support BOTH an analog display (with
a connector adapter) and a digital display. A DVI-I port has both the
digital signals and the analog signals present at the DVI connector. To
use the analog signals, you only need a connector adapter, or, in some
cases, a "splitter cable" (to use BOTH the analog and digital signals of
the DVI port simultaneously). The only reason for a vendor (ATI) to
supply a DVI to VGA connector adapter is to allow use of the analog part
of the DVI port. The DVI spec is non-specific as to whether the analog
port is the "same" video as the digital signal, or whether the analog
port is an entirely separate channel (e.g. for a dual-display
configuration).
Note that quite a few ATI boards, especially "All-in-Wonder" boards,
have ONLY a DVI connector, and that an adapter must be used to connect
an analog VGA monitor. Clearly, in such cases, the DVI connector is not
for LCD flatscreens only (or even for monitors that require digital
input), as not only do most CRTs not have digital input, but, in fact,
most LCDs are actually analog rather than digital.