With Training packages, in my own games, they are aways restricted in number and are based upon availability/accessability within the campaign if acquisition is attempted after the character creation phase.
Therefore, the number of ranks gained is usually not that great to require the cap at 1st level. Yes, it is very rare for most experienced GM's to actually start their characters at 1st level (I tend to start mine at 3rd), so the problem might rear its head then... but actually acquiring a TP *in game* should be a fairly rare event/opporunity.
I do tend to require the compulsary purchase of at least one TP per level for starting characters (with a maximum of 6 total during the creation phase), this creates a history, and tends to use the majority of a starting characters DP to create a fairly rounded character.
So why is it considered a problem requiring a cap? The downsides of TP's (which I love BTW exactly for the reasons of backround creation, time-savings and realisitc skills coverage) is the downtime (and aging) required to achieve those benefits in game.... and the fact, that even though what you do get is discounted, you don't normally get *exactly* what you, as a player, would wish to get if you were to individually choose the skill ranks from the same equivilent pool of DP. Yes, it enforces rounding of a characters skills to reflect what is expected from that TP, and that is a good thing... but many of those skills simply will not be commonly used from a player's perspective.
For character creation, the downtime spent achieving the skills provided by TP, is meant to be reflective of the benefits of experience gained whilst practicing that activity that the TP represents balanced by the loss of adventuring experience that the character might have recieved in the same period of time. Therefore, whilst a student might recieve a doctorate after taking 2-3 TPs...by 3rd level, they have missed out on an equivilent of several years of adventuring time, which could easily have got them 10+ levels!
No, I feel that the problem isn't the cap on ranks gained from TP, rather the potential overlap of several TP that might provide the exact same ranks in the same skills. That can be easily prevented in three ways without requiring a mandatory cap, if you as a GM are concerned about it being a problem in your campaign.
1. Don't allow the same Named TP to be taken twice*
2. If skill ranks acquired in two different TP are optional, then simply state that the player must allocate them to different skills.
3. Ban specific TP.
As I said, IF you consider it a problem as a GM. Personally, this might only occur with combat skills.. but for the most part overspecialisation of this magnitude causes deficits elsewhere in a character.
*SM(P) has several, IIRC, Engineering, Medical and Tech-based that can, though these are basically differing levels of the same TP for qualifying requirements for a more advanced TP (and could easily be renamed as seperate TP).