Hmm...I didn't know this. Although on regional trains (Przewóż Regionalny) such as between £ódż and Warsaw you can only pay cash.
Between £ódź and Warsaw there are TLK trains by PKP Intercity and InterRegio train by Przewozy Regionalne. The TLK train on this route (if I remember it well - only in 2nd class) are an exception from all the TLKs - they don't have obligatory reservation of seats. It is because many people use them to get to work every day. They usually buy a single ticket for total month. To have a seat guaranteed, they would have to visit the ticket office every day to obtain a seat ticket for the train they are going to go by. So all the trains of PKP Intercity company, except the ones on the route £ódź-Warsaw in 2nd class, have obligatory reservation.
In Przewozy Regionalne the situation is different. As I know, the reservation is avaliable only for RegioExpress trains (they have Regio, InterRegio and RegioExpress) and it's not compulsory.
Although on regional trains (Przewóż Regionalny) such as between £ódż and Warsaw you can only pay cash.
The fact that conductors have mobile terminals does not mean that you can pay there by card. They are only for printing tickets, in some cases - for specific seats in specific train, in other ones - for specific route and time.
Generally train tickets in Poland are not for a specific train, but for a specific route and time. If a ticket isn't tied with a seat reservation (so in Przewozy Regionalne and in 2nd class in Warszawa-£ódź TLK trains) you can choose a later train or a connection on the same route with changing trains and a ticket will be still valid, unless it will expire. Tickets with seat reservation (so for most or PKP Intercity trains) are always valid for the time interval corresponding to the departue and arrival of the specific train, so for example if you are late, you can only obtain a paper confirming that a ticket wasn't used and return the ticket.