This looks more than a coincidence than anything else. Romans did conquer lands which could not grow wine, e.g. the British Isles: the climate of Atlantic-facing areas of Europe is reputed to have been somewhat warmer than usual in Roman times, but this does not mean that winegrowing was actually possible, let alone done by Roman colonists. In fact, archaeological evidence points at massive imports of wine rather than local production. Conversely, Romans did not conquer some neighbouring lands where winegrowing could be done, e.g. what is now Ukraine.
According to Edward Luttwak, the pattern of Roman conquest is best explained through strategic and economic reasons, of which winegrowing is not a significant part. In his analysis, Rome first had an expansionist phase which was building an Empire (in fact, though not in name): to the core group of Roman provinciae was adjoined a vast number of client states, who were subservient to Rome and served as buffer against hostile foreigners, especially raiders from Germanic people. In the client state system, that state is responsible for its own policing, and Roman citizens are safe; the cohesion of the Empire can be maintained with a relatively small number of highly mobile legions.
This expansionist phase mostly ended after Augustus' reign. Afterwards begins a phase where external boundaries do not move much; there were some external campaigns but only in some places, and conquests in Parthia and Dacia proved too expensive to be maintained in the long term. During that phase, client states were gradually converted into provinciae, which allowed for direct taxation and thus a large increase in revenues for Rome; however, it also implied ensuring the safety of these new taxpayers, hence the limes: a linear, static defence system at the boundary. This process was mostly complete by the third century AD. The abandoning of the "mobile legion" system implied also a stop to expansionism.
Wine does not appear anywhere in this analysis of Roman strategy. It seems unlikely to serve as a primary motive for expansion. Instead, Rome conquered the neghbouring tracts of land that were already, at that time, harbouring large chiefdoms or states, and thus could be conquered and turned into client states with minimal post-conquest occupation cost. What is true, though, is that Romans were great consumers of wine and tried to grow grapes wherever they could; this can go a long way toward explaining the approximate overlap of Empire and winegrowing areas.