Yes, there are two different products -- DVD Architect 4 and DVD Architect Studio 4.
DVDA Studio 4 can be purchased either by itself or as part of Vegas Movie Studio + DVD Platinum. DVDA can only be purchased with Vegas+DVD (which is also a different product).
DVDA Studio does not appear to have subtitle functionality. DVDA does. If you'd rather have DVDA, you'd have to buy bVegas+DVD, which costs considerably more than DVDA Studio or Vegas Movie Studio + DVD.
If you bought DVD Architect Studio 4 directly from Sony, you could call their customer service and explain to them what happened, and they'd probably let you return it. Particularly if you buy Vegas+DVD instead.